A 2.45 GHz high current pulsed proton source for proton linear accelerator injector was introduced. Hydrogen plasma was obtained using a microwave feeding at the frequency of 2.45 GHz. A 50 keV, 50 mA pulsed beam was extracted by a 3-electrode system consisting of the plasma electrode, suppression electrode and grounded electrode. The characteristics of extracted beam and impedance matching of the transitional waveguide were studied by by CST and PBGUNS codes. The effect of the axial magnetic field distribution on extraction beam was studied by 2D-Poission code. The transmission and reflection coefficients were 0.993 and 0.119, respectively, when the frequency varied from 1.8 to 3.2 GHz. The results show that the total ion current reaches from 0 to 50 A, and the current of the extraction beam reaches from 20 to 50 mA.