The invention provides a detection device for in-place assembly of end plates of a tunnel segment steel mould and a detection method. The steel mould comprises two oppositely arranged end plates and two oppositely arranged side plates, wherein the two end plates and the two side plates are connected to form a rectangular space. The detection device comprises an identification pattern, a correctionassembly and a measuring machine, wherein the identification pattern is used for the calibration of the measuring machine, the correction assembly is used for the correction of the measuring machine,and the measuring machine is used for obtaining the spatial position of the identification pattern and the distance between the identification pattern and the end plates. According to the invention,a detection device for in-place assembly of the two end plates of the tunnel segment steel mould is designed by integrating an image recognition technology, an image comparison technology and a lasermeasurement technology according to steel mould assembly requirements, and high-precision distance measurement is realized so as to judge the correctness of the assembly state of the steel mould. Meanwhile, the technology also improves the practical operability on site and achieves the purposes of convenience, high efficiency and low cost.