The existing metro portal steel ring detection and data processing method is slightly complicated and have no ability to resist gross errors. As a result, based on the study of precision detection method of the portal steel ring, a RANSACbased onestep solution for the spatial shape fitting parameters of the metro portal steel ring is proposed. The spatial shape analysis and quality evaluation of the metro portal steel ring can be realized through the portal center, radius, flatness, verticality and roundness. The proposed algorithm is programmed with the C# programming language and the SQL Server database as tools; the Leica TM30 measuring robot is used to detect the steel ring of the portal door of Wutaishan Station on Nanjing Rail Transit Line No.5; and the measured data are calculated and analyzed. The results show that the proposed method can resist the disturbance of abnormal value to the portal steel ring spatial shape fitting results, which indicates that it is a more effective and practical method for detection and data processing of the metro portal steel ring.