The invention discloses a light mixing method for the controllable brightness adjustment range of an LED colorful light source. The method comprises the steps of firstly, calculating the ratio of eachprimary color light to the maximum brightness of the primary color light, and judging whether a corresponding light source needs to be output or not according to the ratio, and completing the color mixing step; secondly, adopting all primary colors required to participate in color mixing as a set, calculating to obtain the ratio of a lowest brightness required by a standard light source to the highest brightness of the light source, and judging whether the adjustment of the color deviation needs to be introduced or not based on the ratio. In this way, the color deviation method can be introduced under the condition that the proportional brightness is very small. The uncontrollable problem caused by extinguishing the basic unit of one certain color when the brightness of the basic unit ofthe certain color is reduced in the prior art can be solved. As a result, in a coordinate system configured to approach an original point, the adjustment range is enlarged, and the ornamental value ofa user is greatly improved.