Summary: A statistical model describing measuring error series of tracking radar is built. By analysing test data of tracking radar accuracy recorded, we present a linear regression-autoregressive mixing model with slowly varying variances, which describes tracking radar measuring error series as follows: \[ y_t= \beta^\tau u_t+ \sigma_t \varepsilon_t, \quad \varepsilon_t +\varphi_1 \varepsilon_{t-1} +\cdots +\varphi_p \varepsilon_{t-p} +e_t. \] The method demonstrates the effectiveness of the model.