A plant illumination apparatus includes a light source module including a first light source and a second light source generating lights having different wavelengths, an environment-detecting module detecting an external environment to obtain a real-time environment parameter, and a control module connected to the light source module and the environment-detecting module. The control module includes a processor unit and a storage unit storing a database of plant growing environment parameters. The processor unit loads at least one preset growing environment parameter corresponding to a plant growth timing from the database of plant growing environment parameters, and compares the preset growing environment parameter with the real-time environment parameter to output at least one comparison result. The processor unit adjusts the first light source and the second light source according to the comparison result, so that an adjusted environment parameter matches the preset growing environment parameter.