Electric field induced optical second harmonic generation (EFISHG) measurement at the laser wavelength of 1000nm and 1080nm is conducted to investigate the carrier behaviors in PCPDTBT and PC71BM bulk heterojunction organic solar cells (OSCs). We find that the response time for electrode charging through the external circuit in +1V and -1V are almost identical but the response time for the Maxwell-Wagner-type interfacial charging is different in +1V or -1V. We find that the accumulated charges of PC71BM is more than the accumulated charges of PCPDTBT and consequently affects the efficiency of the bulk heterojunction OSCs.