Abstract: Improved particle-in-cell(PIC) algorithms were proposed, including volume weighting cloud-in-cell model, geo-metry profile considered explosive electron emission model and divergence error diffused perfectly matched layer boundary, which increased the precision of the algorithm and decreased the numerical noise. Based on the improved models, an user-friendly, 2.5-dimensional PIC code UNIPIC has been developed, which could be used to simulate high power microwave source devices and used for their geometry optimization in x-y, z-r and r-φcoordinate systems. The simulation results of relativistic magnetron, magnetically insulated line oscillator, virtual cathode oscillator showed good physics image and beam-wave interaction characteristics.