In order to optimize the performance of vertical cavity semiconductor optical amplifiers(VCSOA) in different applications and obtain accurate reflectivity with the general calculation method, considering the characteristics of light field distribution inside the device, the equivalent reflectivity of the distributed Bragg reflector(DBR) and the full width at half maximum of the beam in the device were obtained by using angular spectrum theory and transmission matrix method. The theoretical analysis and experimental verification were carried out. The results show that the equivalent reflectivity increases with the increase of structure period. However, when the period is greater than 25, it will not change any more. Compared with the case of normal incidence only, the revised equivalent reflectivity of DBR is less 2%~4%. Equivalent reflectance decreases with the increase of full width at half maximum θFWHM. The study provides theoretical guidance for accurately calculating the effect of stack number on equivalent reflectivity of DBR and optimizing the performance of VCSOA.