The theoretical model which transverse magnetic (TM) polarization state and transverse electric (TE) polarization state share the same inverted population is built based on the time dependent theory of random lasers. By using the finite difference time domain (FDTD) method to numerically solve Maxwell equations and rate equations, we can obtain the threshold properties for two polarization states. The results show that TM state has a lower lasing threshold than TE state when they don’t share the inverted population, otherwise, the TM state is strongly suppressed. In the competition condition, the threshold for two states changes hardly by changing the surface-filling fraction, but will decrease for TM state when increasing the sample size.