A novel scheme based on light diffraction to generate a triple-well optical trap for trapping and controlling triple-species samples of cold atoms or molecules is proposed. Specialized phase modulation similar to binary phase-grating is implemented by a diffraction device of liquid crystal spatial light modulator (LC-SLM). A continuous and reversible evolution between single-well trap and triple-well trap is investigated. Corresponding experiments are performed and the results are in agreement with theories. The results show that the proposed scheme has a controllability advantage, which is beneficial to load and control triple-species samples in cold atoms or molecules experiments.