Abstract: The effects of applied potential on the sulfide stress cracking (SSC) resistance and hydrogen permeation behavior of C110 steel and the cracking mechanisms were discussed by the SSC resistance test and hydrogen permeation test. The results show that when the loading stress was 85% of yield strength under no applied potential, C110 steel passed the test according to the NACE TM 0177-2016 standard method A indicating that C110 steel had a good SSC resistance performance. When -100 mV or +100 mV potential (relative to open circuit potential) was applied, fracture occured to the C110 steel samples and the SSC sensitivity was enhanced. When anodic potential was applied, the mechanism of cracking was related to anodic dissolution type. When cathodic potential was applied, the mechanism of cracking was related to cathodic hydrogen evolution type. With the growth of cathodic potential, the steady-state hydrogen permeation current density, the subsurface hydrogen concentration and the SSC sensitivity of C110 steel all increased.