The invention provides a device for measuring the charge-to-mass ratio of a separate charged-particle, which can measure the charge-to-mass ratio of a separate charge-particle. The device is simple in structure and easy to operate. Unlike the currently available device whose measuring objects are all charged clusters rather than a separate charged particle, the device of the invention is able to obtain more accurate measuring results. The device of the invention comprises a uniform electric field generation device and a grating range measurement system. The uniform electric field generation device is used to enable the charge particle to make uniformly accelerated motion in the uniform electric field generated by the uniform electric field generation device; and the grating range measurement system is used to obtain the motion trajectory of the charged particle in the uniform electric field. Based on the corresponding relationship between the trajectory of uniformly accelerated motion and the imposed external force, the charge-to-mass ratio of the charged-particle is determined.