The project was started in order to solve the problem of periodic outbreaks of cyanobacteria in Chaohu Lake, and to improve the state of long degradation cycle of low-density polyethylene materials. In this study, the low density polyethylene (LDPE) was taken as matric, and algae powder was taken as bio-material. Maleic anhydride grafted polyethylene (PE-g-MAH) was used as compatibilizer, and polyethylene wax and white oil were used as lubricant. The dosages of compatibilizer and algae powder were selected as the two factors in this paper. Mix the experimental materials in a certain proportion, then prepare the composite particles by double-screw extrusion method, obtain the samples by injection. By using ultraviolet-visible spectroscopy (UV-Vis) and fourier transform infrared spectrometer (FTIR Spectrometer), we can learn the spectral characteristics of materials, and analyze the structural changes of composite materials in the preparation, thus we can determine whether this method is feasible in preparing this composite in advance. Meanwhile, by using mechanical performance testing and scanning electron microscopy (SEM) as auxiliary means, comparing with the results of spectral analysis, we can adequately analyze the effects of algae powder and compatibilizer content on the structure and properties of the composite. Results showed that the absorption peaks appeared at 260nm and 620nm when using ultraviolet-visible absorption spectroscopy to analyze the separated liquid components obtained from the algae. It is proved that the algae contains phycobiliprotein and can be used as the bio-material in the preparation of composite materials. The characteristic peaks of amido bond has appeared respectively at 1 630, 1 540 and 1 440 cm-1 when using fourier transform infrared spectrometer to analyze the substances that participate in the reaction, which was in line with the peak law of amide bond; and the characteristic absorption peaks of O—H appeared near 3 300 cm-1, which can further verify the existence of the active site of algae powder. It can be seen in the infrared spectrum of maleic anhydride, the characteristic peaks of CO group appeared at 1 850 and 1 740 cm-1, and the characteristic peak of stretching vibration of C—O—C in cyclic anhydride appeared around 1 200 cm-1. However, the characteristic peaks of amide bonds, H—O group and maleic anhydride except the characteristic absorption peak of polyethylene were weakened or disappeared when using Fourier transform infrared spectrometer to analyze the composite material obtained by reaction, and it can be speculated that the maleic anhydride has an open-loop esterification reaction with —OH, and the maleic anhydride plays a role in connecting two different reaction systems in the preparation of biological composites. In addition, it can be investigated intuitively by using scanning electron microscopy that the increase of algae powder content will lead to the aggravation of clumping in the composite system, and the addition of compatibilizer enhanced the adhesion of the interface of the composite system. The mechanical property test showed that the mechanical properties decreased with the increase of algae powder content, especially the decrease of impact properties with 54.10%. Results showed that when 15.00% of algae powder was added in the composite, the tensile strength, flexural property and impact property of the composite first increase and then decrease with increasing of compatibilizer content. Therefore, the results of scanning electron microscopy and mechanical properties verify the foresight and correctness of spectral analysis results from the side, avoiding the waste of resources caused by blind experiments and other issue. The optimized conditions for preparation of the bio-composite were determined with 15.00% of algae powder, 3.00% of PE-g-MAH, 3.00% of polyethylene wax and 1.00% of white oil. The mechanical properties of the bio-composite prepared under this condition were 11.70 MPa of tensile strength, 20.00 kJ·m-2 of impact strength, 8.80 MPa of bending strength, and the bending modulus was 220.00 MPa.