With the 2.5D fully electromagnetic particle-in-cell code, a P-band hybrid magnetically insulated transmission line oscillator(MILO) was proposed and investigated by using the advantages of both tapered MILO and load-limited MILO. For the hybrid MILO, one extractor vane is taken place by three ones with tapered depth to form a taper section in the load-limited MILO. This provides a better match between the electric field of the main slow wave structure and the electric field of the output coaxial transmission line in order to increase the output microwave power. The simulation results show that a 640 MHz, 4.27 GW high power microwave in TEM mode can be obtained when the beam energy is 550 keV and current is about 57 kA. The efficiency is about 13.6%. The MILO starts to oscillate at 4 ns, a