Abstract: There is a lack of a controller in existing DC fault simulation models of ultra-high voltage direct current（UHVDC） projects.Also their pure numeric simulation is slow.Thus a semi-analytical simulation method is proposed for a multiterminal hybrid UHVDC.First,practical models of both conventional DC and flexible DC converter are established considering controller dynamics.Secondly,a DC single-pole grounding fault simulation model for a typical three-terminal hybrid UHVDC is built and then analyzed using a multistage semi-analytical method （MSAM）.In the MSAM,the simulation period is evenly divided into several small intervals,and an approximate analytical solution is obtained for each interval.The advantages of analytical methodology and a numerical algorithm are united in MSAM,where parallel computing is also easy to implement.Lastly,the simulation results of the MSAM are compared with those of PSCAD/EMTDC and common numerical methods （Euler method and 4th order Runge-Kutta method）.The simulation waveforms of the MSAM match with PSCAD/EMTDC very well with a significantly higher simulation speed than the common numerical methods.