Abstract: With the combination of three gain mechanism of double tapered structure, choke and impedance transition based on the two present magnetically insulated transmission line oscillater (MILO) models, a new improved type MILO has been designed through numerical simulation using two and a half dimensional particle in cell (PIC) code. Its peak output power is 6GW in L band when input voltage is 550kV and input current is about 35kA.