To achieve a sufficient light dose and control the light field distribution in capsule under battery-powered, experiments are conducted using digestive tract tumor cell model and tumor-bearing mice model. The killing effects of Gaussian, non-uniform, and uniform light fields produced by light-emitting diode (LED) arrays on tumors are compared, identifying the effect of uniform light field as the optimum. To achieve an LED array with a uniform light field output under capsule size, a three-dimensional mathematical model of the LED array's light field is established to deduce optimum irradiation distance and spatial distribution of the capsule light source. The model indicates that an equilateral triangle LED array with a distribution radius of 7 mm can achieve uniform light field when the irradiation distance range is 7.1?8.8 mm, the optimum irradiation distance is 7.8 mm. The fit between the real LED array results and the mathematical model output is excellent, with a fit coefficient of 0.9934. Results show that the capsule-based photodynamic therapy light source with LED array can achieve uniform light field within the working distance and complete the photodynamic effect. This study successfully developes a prediction model for LED array light field distribution, provids a useful research tool for the medical application of LED light sources.