In this study, soil model animal C.elegans was used as test subject, and the effects of different particle sizes and concentrations of polystyrene (PS) microplastics on the feeding preferences of C.elegans under short-term and long-term exposure conditions were studied. The results showed that, the feeding preferences of C.elegans on B. amyloliquefaciens JX1 (X1) and P. fluorescens Y1 (Y1) did not change significantly after short-term exposure to PS microplastics of 1 μm and 5 μm at 1, 10 and 100 mg/L; At the concentrations of 1, 10 and 100 mg/L, PS microplastics of 5 μm could change the feeding preferences of C.elegans on X1 and Y1, and significantly upregulated the expression of feeding related genes (cat-4, egl-4, gcy-28, daf-7, dbl-1, tir-1 and tol-1) in C.elegans under long-term exposure. The indexes related to oxidative stress in C.elegans were all upregulated after long-term exposure to PS microplastics of 1 μm and 5 μm at 100 mg/L, but had no significant correlation with the particle size of PS, suggesting that oxidative stress damage may not be the direct way responsible for the effect of PS microplastics on feeding preference of C.elegans. These results suggested that PS microplastics could affect the feeding preference behavior of C.elegans by regulating the functional genes related to feeding preference.