Zhoushan multi-terminal VSC-HVDC project will be the first DC transmission project with five converter stations in the world which is based on modular multilevel converter (MMC) technology. To study the overvoltage of each converter station, overvoltage mechanism of AC and DC switchyard are analyzed in detail based on this project, and overvoltage levels in typical faults such as single-phase-to-ground fault at the valve side of converter transformer and at the valve side of converter reactor, DC pole line ground fault, ground fault at the valve side of DC smoothing reactor and DC to DC pole line fault are calculated based on the MMC-HVDC model with five stations. Results show that the maximum overvoltage for AC bus at the valve side of converter transformer is 360 kV; the maximum overvoltage for DC bus at the line side and at the valve side of the DC smoothing reactor are 370 kV and 369 kV respectively; the maximum overvoltage of the neutral point of star reactance grounded branch and converter reactor are 188 kV and 235 kV respectively; the maximum energy of arrester CB and D are 1.258 MJ and 1.655 MJ respectively. The research results will provide important basis for the insulation coordination of station devices.