An instrument for dynamically observing the evolution behavior of the slope topography. The dual hosts emit parallel, equal-height and overlapped laser planes from different directions, and project the laser planes onto a slope landform. The image acquisition device shoots the slope landform with the projected laser lines at an angle perpendicular to the laser-planes. Then a video screenshot can be formed and imported into a computer to form a three-dimensional map. Finally, the volume, slope gradient and other parameters of the slope body can be obtained. As the knobs on the mechanically micro-adjustable host of the topography meter are turned, the laser-planes can become precisely equidistant and parallel. A novel topography meter is disclosed, which can conveniently calibrate the spacing and angle of the linear lasers and accurately observe all landforms including the local deep trenches on an eroding slope.