The invention discloses a device and a method for quickly measuring slope inclination. The device comprises a bracket arranged on a ground monitor pier, a supporting frame arranged on the bracket, an inclination measurement mechanism which is arranged in the supporting frame and is used for measuring changes of the slope inclination, and an azimuth measurement mechanism which is arranged at the top end of the supporting frame and is used for measuring changes of the slope azimuth. The method comprises the following steps: 1. constructing the ground monitor pier of a slope; 2. assembling a levelling measurement device; 3. recording an initial azimuth alpha of the slope; 4. determining whether the slope is inclined or not; 5. recording an azimuth alpha' after the slope is inclined, and acquiring the slope azimuth changing information; and 6. acquiring an inclined angle beta after the slope is inclined. According to the device and the method, operation steps are simple, the slope azimuth change can be observed by the azimuth measurement mechanism, change of the slope inclined angle is acquired through equivalent rotation of a cylindrical level gauge of a rotary platform in the inclined angle measurement mechanism, the azimuth and inclined angle of slope inclination can be quickly and accurately acquired, and the slope inclining situation can be analyzed.