The invention relates to a multi-beam deformation detecting device which comprises a probe, a digital signal processor DSP, a personal computer PC, a laser group and a prism reflection target, wherein the prism reflection target is arranged on a point to be tested, the probe and the laser group are arranged on a measuring point, a laser beam group emitted from the laser group is reflected through the prism reflection target by adjusting the laser group and then forms an overlapped light spot on the probe, a barycenter of the overlapped light spot is determined by utilizing a photoelectronic tracing macro pixel iteration barycenter method, and the deformation of the point to be tested is further determined through the barycenter offset distance. The invention can effectively avoid the influences on environmental change, air turbulence and stray light, can realize long-term online monitoring, and has accurate measurement data, high detection precision, simple structure, low cost and convenient operation.