Gypsum breccia, having such characteristics as low strength, heterogeneous quality and high local compressibility, belongs to complex soft rock of special type. On basis of the gypsum breccia geology of Z5 bid section of Taihangshan tunnel, the authors study on the geological background, origin and engineering behavior of gypsum breccia in the paper, placing the emphasis on the presentation of the results of the insitu experiments on the engineering behavior of gypsum breccia.