Abstract: The discoloration of PVC core material often occurs during the curing process of wind power blades. In order to study the effect of PVC core material discoloration on the mechanical properties of composite materials, four kinds of 45 mm thick PVC sandwich structured test panels with different degrees of discoloration are prepared, and four-point bending tests on sandwich structure are carried out to compare the bending failure load, ultimate shear strength and ultimate fatigue performance of PVC sandwich structure with different discoloration degrees. The results show that the average bending failure load and shear strength of the severely discolored PVC sandwich structure are reduced by 7.3% compared with those of the normal PVC sandwich structure without discoloration. The bending fatigue performances of the severely discolored PVC sandwich structure and the normal PVC sandwich structure are equal to or better than that of the normal sample. No obvious structural collapse is found inside the discolored PVC sandwich foam by electron microscope.