LCC conversion between rectification and inversion by voltage reversal may force multi-terminal HVDC transmission system to be power interrupted for a short time. So a connection scheme based LCC for parallel three terminal HVDC transmission system is presented, the possible operation modes and conversion methods are analyzed, the control sequences of pole conversion and DC voltage controlling station input and output and emergency exit strategy for fault pole are presented. Based on the platform of PSCAD/EMTDC, the three terminal HVDC simulation model is built to carry out the simulation on pole conversion, DC voltage controlling station input and output, and emergency exit of fault pole. The simulation results show that power reversal of one converter station based the multi-terminal HVDC would not affect others station, and could isolate fault devices safely to recover the stable operation of sound system quickly. This work is supported by National Key Research and Development Program of China (No. 2016YFB0900603) and Science and Technology Project of State Grid Corporation of China (No. 52094017000W).