The invention discloses an LED blackboard lamp blue light prevention method which comprises the following steps: step 1, primary light distribution: a lens is arranged to reflect and refract light emitted by an LED light source to obtain primary emergent light; step 2, secondary light distribution: a reflection cavity is arranged to reflect the primary emergent light in the first step, and secondary emergent light is obtained; step 3, third-time light distribution: a transparent microcrystal plate is arranged to conduct diffraction and diffuse reflection on the secondary emergent light in the second step, a plurality of granular protrusions are arranged on the emergent face of the microcrystal plate, and third-time emergent light is obtained; and step 4, a layer of titanium dioxide light guide film is plated on the emergent surface of the microcrystal plate, and refracting, filtering and reflecting is carried out the third emergent light in the step 3 to obtain soft and uniform illumination light with less glare and no blue light hazard. Light is distributed for two to three times and then scattered by the microcrystalline plate, so that the illumination uniformity of the blackboard surface can be improved, the blue light harm is effectively reduced, the glare is reduced, the use feeling is good, the emitted light is soft, and the blue light prevention effect is good.