There are many capacitive and inductive components in converter station for ±800 kV DC power transmission system, which is easy to cause overvoltage phenomenon when a short circuit fault occurred. Research on the characteristics of overvoltage under various operation and fault conditions to ensure the system''s safe and stable operation is very important. A simulation model of the UHVDC power transmission project from Yunnan to Guangdong is built by using PSCAD software. To carry out this research, two typical faults in convert station are chosen:the short circuit fault between the top of convert valve and neutral bus, and single-phase ground fault occurred at the side of converter transformer. Research results show that higher overvoltage appears on the non-faulty pole when short circuit fault between the top of convert valve and neutral bus; among four upper rectifier bridge side of connected winding of convert transformer, the highest overvoltage appears at upper rectifier bridge side wye-wye connected winding of convert transformer when single-phase ground fault occurred.