For realizing optimal performance, knowing the photon absorption cross-section of alkali atoms is significant in a wide range of fields, such as atomic clock, atomic magnetometer and atomic spin gyroscope. By analyzing the pressure broadening and shift, natural broadening and Doppler broadening of the absorption line of 87Rb D1 line, the numerical simulation of photon absorption cross-section of 87Rb D1 line is conducted. Based on the results of numerical simulation, natural broadening is found to be much smaller than pressure broadening and Doppler broadening in general. The pressure broadening becomes the dominant factor of broadening for high pressure of buffer and quenching gases, while the Doppler broadening is dominant for low pressure of buffer and quenching gases. The results of numerical simulation demonstrate that, with the increasing broadening of absorption line, the number of peaks of the photon absorption cross-section decreases from four to one gradually, and the amplitudes of these peaks decline in the meantime.