Low-level light therapy （LLLT） based on light-emitting diode （LED） light sources is a rapidly-developing and non-invasive light therapy technology. In contrast to a laser， LED phototherapy can easily produce a larger treatment spot area， while achieving almost the same treatment effect. When designing LED phototherapy equipment and formulating phototherapy plans， too large an angle between the edge light and skin could affect the light penetration effect. Therefore， a skin model is required to analyze the light penetration for a large area of light spots. First， this study identified a general skin model sample based on the optical properties of skin tissue. Then， Monte Carlo simulation was used to trace the light emitted by the LED light source， and the wavelength distribution of light and different divergence angles were analyzed. Finally， the reliability of the sample model was verified based on the skin parameters of the human shoulder， forearm back， and buttocks. The simulation results demonstrated the transmission of a large-sized LED spot in the skin. Experimental simulations of different skin parts proved that the spot divergence half-angle needs to be controlled within 30°. This provides an important reference for the field of LED light therapy.