Controllable and effective irradiation of lesions is among the key factors that affect the potency of photodynamic therapy (PDT). An optimization method for the irradiance distribution of treatment was proposed which can be used to improve the efficacy of PDT and allow more lesions to receive the desired irradiance level in a single therapy session. With the proposed digital illumination binocular treatment system, the preferred surface normal vectors, irradiation angles, as well as area and weight coefficients of lesions can be achieved and used as characteristic parameters to optimize the irradiation direction. Two port-wine stain phantom experiments were performed. The comparison of the illumination area between preoptimization and postoptimization showed that the proposed method can effectively guide the light source control, improve the distribution of light dose, and increase the effective treatment area.