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