This paper presents the simulation of a vane-type magnetron using the commercial electromagnetic software Particle-in-Cell (PIC) solver in CST. The magnetron mainly consist of 18 anode vanes without strap. The resonance frequency has been selected in X band since it has a long production history enabling a ready comparison of computed and measured results. Simulation of magnetrons has been improved by changing dimensions of cavities, optimizing voltage and applied magnetic fields values. The aim of this work is to tune the operation frequency of magnetron under the constant electric field and the magnetic field between the anode and cathode.