A control method for a light therapy device, including steps of: set a light dose range (1-4 J/cm2) required by an illuminated portion under a skin surface； calculate an appropriate intensity range outputted by a light source based on the set light dose, an illuminated time, and a proportion of light beam shape variation between the light source and the skin surface； build a corresponding relation between the appropriate intensity range and an ideal illumination range for the skin surface； measure an illumination of the skin surface, and monitor an output light intensity of the light source based on the illumination, ensuring that a light intensity outputted by the light source is a set ideal light intensity whereby, a light dose transmitted from the light therapy device to the illuminated portion could be kept in the set light dose by simply controlling the illumination to be within the set illumination range.
