The invention relates to the technical field of plasma three-dimensional diagnosis, in particular to a plasma three-dimensional information diagnosis system in the process of material surface treatment. The system comprises a computer, a first plane reflection mirror, a focusing lens, an incident slit, a second plane reflection mirror, a first spherical reflection mirror, a convex grating, a second spherical focusing mirror and a surface array detector. The system of the invention combines the rotating, scanning and collecting of plane reflection mirrors with an Offner imaging spectral diagnosis system, and realizes the acquisition of plasma signals in different areas through the scanning of the first plane reflection mirror. The scanning process is simple and rapid. Through the Offner imaging spectral diagnosis system, the light-splitting and detecting of the acquired information can be realized, and finally the diagnosis of the three-dimensional information of the plasma in the cavity is realized. The system can realize the acquisition of the imaging signal and the two-dimensional spectral information in the cavity outside the surface treatment chamber, wherein the spectral signal corresponds to the formed image, providing an on-line detection means for the surface treatment process.