The hot electron injection effect plays a vital role in many research and applications involving light energy conversion, such as photoelectric catalysis and optoelectronic devices. The improvement of hot electron injection efficiency is the key to promoting device performance. The establishment of a model of the hot electron injection process and the quantitative calculation of the hot electron injection efficiency are very important for improving the efficiency of hot electron injection. On the basis of the Fowler theoretical model, the hot electron injection process was devided into three parts for quantitative analysis: hot electron generation, transmission, and emission. The effects of incident photon energy, noble metal nanoparticle size, and the Schottky barrier height on the hot electron injection efficiency were simulated and calculated. The simulation results show that there is a positive correlation between incident photon energy and hot electron injection efficiency; noble metal nanoparticles with a radius of about 5 nm have the best hot electron injection efficiency; the hot electron injection efficiency gradually decreases as the height of the Schottky barrier increases. The results of this research deepen the understanding of the physical process of hot electron injection and provide theoretical guidance for the design of plasma photocatalysts and optoelectronic devices.