Abstract: In order to essentially improve microwave output power and efficiency, a new idea about magnetically insulated transmission line oscillator (MILO) is brought forward, which use most of the load current to produce microwave. A new type of MILO that comprises traditional MILO and VCO, called MVO, is designed and simulated by 2D PIC method. The results show that both parts of MVO work well and the main frequency accords with slowwave structure (SWS), and that MVO yields an output power of 500MW higher than traditional MILO in the case of 25GW(at 500kV) inputpower with the efficiency enhanced from 6% to 8%.