Herbicides have been widely used because of their rapid and effective weeding. But it will also cause a certain degree of pollution to the environment and the crops, and it is often found that the misuse of herbicides causes the fruit trees to be poisoned in the process of agricultural production. Metolachlor is a selective amide herbicide which is widely used in upland crops, vegetable crops, orchard and nursery. According to the relevant literature, the methods of Metolachlor residue detection mainly include Gas chromatography (GC), Gas chromatograph-mass spectrometry (GC-MS), Solid phase extraction (SPE) and so on. The analysis of metolachlor residues based on absorption spectroscopy has not been reported in literature. This paper presented the absorption spectroscopy and its derivative spectrometry to detect the metolachlor pesticide residues in the apple juice. First, the absorption spectrum of different concentration of metolachlor were recorded by spectrophotometer, and it was found that there was a distinct absorption spectrum peak at 266 nm. The relationship between the pesticide concentration and absorbance was obtained by fitting analysis on the absorption spectrum of metolachlor, and the function equation was deduced as y=2.147 09x+0.031 98, and the correlation coefficient was 0.998 5. Second, the absorption spectrum of mixed solution of apple juice and metolachlor were studied by spectrophotometer. Compared with the absorption spectrum of apple juice, the metolachlor characteristic peak at 266 nm was also found in the absorption spectrum of mixed solution. The model function between absorbance and metolachlor concentration in apple juice was further obtained as follows: y=0.704 9+0.826 8x, its correlation coefficient was 0.991 1. It can be seen that when the residual amount of metolachlor in apple juice was very low, the absorption spectrum characteristic peak of the pesticide was not obvious. Third, in order to further improve the detection effect, the first derivative processing of the absorption spectrum was carried out, and the first order derivative absorption spectrum of the mixed solution were then obtained. Compared with the derivative absorption spectrum of apple juice, the derivative absorption spectrum of mixed solution of apple juice and metolachlor pesticide had two distinct spectral peaks, which were located at 269 and 276 nm, respectively. In order to further analyze the relationship between the metolachlor content and the peak value of the derivative absorption spectrum of mixed solution, the metolachlor content and the absorbance of derivative spectrum were linearly fitted, and the corresponding prediction model in 269 nm was deduced as y=0.005 3-0.090 6x, and the correlation coefficient was r=0.992 5. The prediction model corresponding to 276 nm was deduced as y=-0.000 769-0.302 8x, and the correlation coefficient was r=0.990 6. At last, in order to verify the accuracy of the prediction model obtained from the absorption spectrum and its first derivative spectrum, five different concentrations of the mixed solution of metolachlor and apple juice were configured and tested under the same experiment condition. The absorbance value at 266, 269 and 276 nm were substituted into the model function respectively, and the predictive value of the metolachlor concentration can be obtained, the average recovery rate can be further calculated according to the actual metolachlor concentration. The calculation results were as follows: the average recovery rate of the absorption spectrum at 266 nm was 104.68%, and the average recovery rate of the derivative spectrum at 269 nm was 104.59%, and it was 105.18% at the absorption peak of 276 nm. The limit of detection (LOD) and limit of quantification (LOQ) parameters were calculated by analyzing the detection model of metolachlor in apple juice. The LOD and LOQ of the original absorption spectrum were 0.014 8 mg·mL-1 and 0.049 2 mg·mL-1, respectively. And the minimum values of LOD and LOQ corresponding to the first derivative absorption spectra were 0.001 5 mg·mL-1 and 0.004 9 mg·mL-1, respectively. The results showed that absorption spectroscopy was fast and feasible for the detection and analysis of metolachlor residue in apple juice, and the detection effect was better after the derivative operation of absorption spectrum.