Identification of tire cornering properties is the base of vehicle dynamics stability control, however, tire side slip angle estimation accuracy based on dynamic model goes worse because of the effects of roll steering and compliance steer under the extreme driving conditions. In order to provide technical means for research on steering wheel angle and wheel side slip angle observation model under the extreme conditions, this paper presents a test method for tire side slip angle based on the direct vision measurement of steering wheel angle and the vehicle body attitude. The test principle of the side slip angle was firstly analyzed, then the roadway test system was established based on the high precision, double antenna differential GPS and the real time image processing device CVS 1456. On the basis of the calibration of the test vehicle steering system gear ratio, both the pivot steering test and the small lateral acceleration test showed the good consistency of the results of the steering wheel angle based on image acquisition with the hand wheel angle. In addition, the circular acceleration deceleration tests showed that the test vehicle reached the extreme conditions while the lateral acceleration was more than 0.8g, and at this time the steering wheel angle curve with image acquisition method fluctuates and reflects the effects of roll steering and compliance steer, so comprehensively the test vehicle has understeer characteristics. The roadway tests indicate that the method proposed is effective and practicable.