Enhancing the sensitivity of the miniaturized spin exchange relaxation free (SERF) atomic magnetometer for weak magnetic detection research is a difficult problem at present. A structure of sensitivity enhanced vapor cell based on Fabry-Perot cavity was proposed to solve this problem. With the principle of Fabry-Perot cavity resonance and theory of light transmission matrix, the amplification factor of optical rotation angle of emitted laser was studied in theoretical analysis and numerical simulation. The results of theoretical analysis and numerical simulation show that as the number of laser transmission round trips in cavity increases, the amplification factor of output rotation angle increases linearly in the initial stage then tends to a maximum value. Ideally, the maximum value is 16 and it is determined by the structural parameter of Fabry-Perot cavity. Besides, the absorption caused by alkali metal atoms spin collision and cavity off-resonance reduce the amplification factor in different ways. Numerical simulation results show that the reduction of amplification factor is close to 50%, while the off-resonance is π/32. This sensitivity enhanced vapor cell is easy to integrate, and provides a new perspective of sensitivity enhanced atomic magnetometer and thoroughly understanding of spin collision in alkali metal vapor cell.