The deformation information in North China is weak. It is necessary to avoid introducing systematic errors but to assess the accuracy in the calculation of the strain field. In this paper, the refined multiquadric function and the spherical integral strain method are used to construct an unbiased strain calculation model. The strain rate of Central North China is calculated based on the CMONOC GPS continuous station velocity data, and the accuracy and credibility of the strain rate are evaluated by the error propagation rate. The results show that it is feasible to calculate the strain rate using the unbiased strain calculation model based on the refined multiquadric function and the spherical integral strain method, and the accuracy and credibility are high.