A method for sensing movement of an object comprises the following steps: obtaining the first image of the object by using an image pick-up device under the irradiation of a non-single wavelength light source within a first period of time, wherein the image pick-up device comprises a lens module and an image sensor, the lens module keeps a longitudinal chromatic aberration of light rays of two wavelengths, and the light rays of different wavelengths are corresponding to different optical object planes; comparing the definition of an image of the first-wavelength light ray in the first image with that of an image of the second-wavelength light ray so as to determine whether the object is close to the optimal object plane of the first-wavelength light ray or that of the second-wavelength light ray; obtaining the second image of the object by using the image pick-up device under the irradiation of the non-single wavelength light source within a second period of time; comparing the definition of the image of the first-wavelength light ray with that of the image of the second-wavelength light ray in the second image so as to determine whether the object is close to the optimal object plane of the first-wavelength light ray or that of the second-wavelength light ray; and obtaining the movement direction of the object based on a relationship of positions of the object in the first period of time and in the second period of time.