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. This work is supported by the Management Science and Technology Project of the Headquarters of State Grid Corporation of China (No. 5100-201955406A-0-0-00).