This paper proposed a new power-split hybrid electrical powertrain to reduce electric loss of single-mode power split hybrid electric vehicle (PSHEV). Different from traditional dual-mode power split mechanism with multi-planetary gear set and multi-clutch, this powertrain is a dual-mode configuration with a single planetary gear set, realizing mode switching by a Synchronizer. The backward simulation method based on global optimization energy management strategy was used to optimize the parameters of the proposed powertrain and Toyota Hybrid System (THS). The optimization results analyzed by energy flow method show that the proposed power split powertrain can reduce the power loss compared with that of THS.