Robust error compensation algorithm for tooth form grinding works of an involute spur gear is proposed. The proposed algorithm is insensitive for the measuring error of the tooth form profiie data. Relationship between indirect measuring quantity ; the grinding error and direct measuring quantity ; the tooth profiie data are expressed by an implicit function. Error propagation analysis for the implicit model is derived using implicit derivative of the model function. Error ellipsoid of the indirect measuring quantity which express the projection of the error hyper sphere of the direct measuring quantity is defined. By taking the structural restrictions of the grinding error model into the least square calculation of the error estimation, the primary axis length of the error ellipsoid became smaller, which means the algorithm became more insensitive for the measuring error. Proposed algorithm was implemented on a in-process measuring system with personal computer. Accurate grinding error compensation was confirmed by experimental results.