In order to evaluate the actual performance of a newly developed aircraft anti-skid braking system, a flight test data analysis method is proposed. Firstly, a test data interpretation process of “pilot review orientation + process interpretation + problem induction + optimization suggestion” is established. Then, a method for calculating the actual wheel speed is developed. And then, the course deviation mechanism of the aircraft during braking deceleration is studied. After that, the phenomenon of course instability caused by deep skid leading to the change of deceleration rate is found in flight test for the first time by comparing the relationship between the slip rate and the deceleration rate of different flights. Finally, the cause of deep skid during braking deceleration is analyzed and some suggestions for optimization of braking control law are put forward. The results show that the developed experimental analysis method can effectively evaluate the performance of anti-skid braking system, which can provide optimization and upgrading reference for the test design and anti-skid braking control law.