In recent years, hybrid energy storage system (HESS) has been studied a lot. Due to the complementary characteristics embraced by each component in the HESS, it is believed that the power supply quality can be improved. Frequently discussed HESS refers to battery-ultracapacitor hybridization, which can be promisingly used as the power supply for Electric Vehicles (EV) where a power train that drives PMSM is generally involved. In this paper, an on-line energy flow split strategy (EFSS) is proposed to timely tune the amount of energy supplements from battery and ultracapacitor respectively. Major contribution of this paper is an EFSS considering the relationship between HESS and PMSM under the influence of SVPWM (Space Vector Pulse Width Modulation) of inverter is proposed, which fits directly into real engineering applications. The proposed EFSS is synthesized with PMSM control algorithm into a TMS320 F28335 based DSP test platform to verify the effectiveness of proposed EFSS. Experiment results show that the proposed EFSS can work well with real PMSM driving system under the presence of load variations.