As shown in previous studies[3],the piecewise-recursive Kalman filter is one of the most efficient and promising approach to decrease the computation requirements of the Kalman filter. In this paper the approach and its influence on the accurancy of estimation and the problem of how to choose the ⊿t(the sampling interval) and ⊿τ = N ?⊿t (the interval between gain-matrix calculations)are considered. In the final portion of the paper，a example is given to show the applicability of the approach.