The effectsof the attitude of circular orbiting spaceborne SAR on the Dopper properties of the echo signals of the centroid of the radar beam are studied in this paper. Expressions are derived for the Doppler frequency centroid, the Doppler frequency modulation rate with the attitude angles of yawing, rolling and pitching. The available integration time and other parameters for SAR mode are also calculated. The analytic expressions are presented simply without mathematical approximation. In the derivation of above expression, Earth rotating is included. The parameters useful in image reconstruction such as range migration and Doppler history are also calculated.