The characteristics of correlation for pseudo-thermal light source have much effect on the quality of image in ghost imaging. The correlated characteristics of pseudo-thermal light have relations with contrast, signal to noise ratio and resolution. On the same condition of experiment, the higher the peak value of the twoorder correlation, the higher the contrast of the image, and the better for the randomness of the pseudo-thermal light, the higher for the signal to noise ratio of the image. Recently, varieties of schemes for correlated imaging have emerged, and pseudo-thermal light correlated imaging based on space light modulator（SLM） has good prospect. The theory of pseudo-thermal light based on different modulation is presented, by which we have simulated the two-order correlation of pseudo-thermal light when different modulations have been sent to SLM, and a conclusion has come that when SLM is modulated by the mixture of phase and amplitude, the peak value of the two-order correlation is the highest, especially when the probability distribution for amplitude is Rayleigh distribution and the phase is evenly distributed between 0~2p, and the peak value of the two-order correlation can come to 2, and the characteristic of pseudo-thermal light is ideal.