Based on the relationship model between the interference fringe shape and the interference angle, a method that applies the four-quadrant detector to recognize the interference fringe shape is presented. The theoretical formula about the shape parameters of interference fringes with the phase difference of signal obtained by the detector has been deduced using the algorithm of area integration for the intensity of interference fringes, and the relationship between the phase difference and the interference angle is given. The dynamic modulation of the interference fringes is realized by using PZT to drive the reference mirror uniformly, and the recognition accuracy of signal phase difference has been improved. The phase difference from 0 to π is achieved with high precision through the ellipse fitting technology, and the identification of the phase difference in the range (-π, π) can been achieved combined with a specific sinusoid and cosine integral calculation, so the measurement of deflection angles can be realized. Comparing with the traditional recognition method that uses the shape of CCD stripe, this method expands the measurement range of the angle, and is more suitable for dynamic measurement. Comparing with high-precision autocollimator, experiment results demonstrate that the precision is 3 arcsec for the range from -300arcsec to 300arcsec, and the measurement owns high precision.