In order to achieve an efficient pulsed power compensation for the ac-sourced pulsed power system, a multifunctional compensator (MFC) of modified T-type semi-two-stage converter is proposed in this article. The power decoupling capacitor is in parallel with one of the dividing capacitors of the three-level ac/dc converter, so that the voltage of decoupling capacitor is able to vary in a very wide range without increasing the voltage stress of the converter. The semi-two-stage compensator achieves better compensation performance and less decoupling capacitor than the single-stage circuit while having higher efficiency and lower converter power rating than the two-stage solution. Operating principles of the semi-two stage MFC are analyzed in detail, and a modulation strategy is presented to achieve two-path power flow between the decoupling capacitor and ac power system. In order to improve the dynamic response of the MFC during the transition between different pulse frequency loads, a power-difference feed-forward control and a dual low-pass filter control are proposed for the compensation. A prototype is built and tested to verify the effectiveness and feasibility of the proposed MFC and control methods.