Abstract: y means of tracking measure of a space vehicle, measuring data of range and range rate can be obtained by using radar or optical instrument. Because of inaccuracy of measuring instrument, surrounding conditions, etc.,system errors are included in the obseryation data of range besides random errors of range and range rate. This paper have obtained a method to estimate the range, range rate and system errors of range by means of setting up a suitable mathematical model, using spline function theory and repression analysis. The calculation using our method is easy.Theory analysis and simulation results indicate the high accuracy of our method.