Experimental and theoretical research on photoelectron yield spectrum play a crucial role in electronic and photo-electronic materials and devices, and the reliable and precise estimation of photoelectron yield via photon energy is very important for detecting microscopic electrical information in photo-electronic materials and devices. Photoelectron yield is defined as the number of electrons emitted by per incident photon. Before this work, the technique was based on the interception of a plot of square root of photoelectron yield versus photon energy for metal-insulator hetero-junction, and that of a plot of cube root of photoelectron yield variation with photon energy for insulator-semiconductor hetero-junction. But, how to intercept the relationship between photoelectron yield and photon energy for semiconductor-semiconductor and metal-semiconductor hetero-junctions has not been known. Besides, many experimental plots of square root and cube root of photoelectron yield against photon energy are available, but none of them is a straight line. In order to obtain a more accurate and reliable barrier height, electrical structure of the junction, the energy level distribution of the energy band offset, defect density in the junction, and the valence band profile through the photoelectric yield spectrum, a reliable and accurate model of photoelectron yield spectrum is established via combining the solution to a differential equation and experimental results. A method is proposed to naturally determine the junction barrier height by using the experimental results of the internal current yield varying with the photon energy. The this method can be used to calculate the junction barrier height as accurately and reliably as possible, and the density and energy level distributions of the effective occupancy states of the electrons in the four junctions are obtained by using this photoelectric yield spectrum model, In addition, based on this model, this paper proves mathematically that the density and energy level distribution of the effective occupancy state of electrons present a peak shape. Therefore, the application prospects of this photoelectric yield spectrum model are demonstrated.