This paper presents the theory of measuring attitudes and analyses the lag of acceleration bias measurement when the vehicle rolls and the sensor drifts, using kinematic Kalman filter with one-antenna GPS/INS measurement system, then brings forward the way to measure directly the vehicle sideslip angle and sensor drift with tow-antenna GPS/INS measurement system, which is used to estimate the vehicle sideslip angle, tire slip angle and tire cornering stiffne ss. The result of experiment shows that the estimation of slip angles and tire cornering stiffness with two-antenna GPS/INS measurement well match the theoretical value, which means the two-antenna GPS/INS measurement as a direct measure method has high estimation accuracy. It can be confirmed that the technology shows unique superiority in the application of future vehicle security systems.