Abstract: We present a method for zoom lens based on reflective phase-only liquid crystal spatial light modulator (LC-SLM). According to the principle of the phase modulation of LC-SLM, incident light waves are controlled by Kinoform, which is writen to LC-SLM. The wavefront of lens is achieved with diffraction. Therefore, the variable focal-length phase Fresnel lens is achieved by changing diffraction distance of calculated Kinoform. Some parameters, such as the diffraction aperture, the diffraction distance and phase levels of Kinoform, are discussed. They are key factors to the variable focallength phase Fresnel lens. Experimental results and the Kinoform of a point light are given. Compared to traditional methods, this method features controllability and accuracy. It will provide a feasible approach for realizing 3D scan display.