The Correlation Interferometer Algorithm (CIA) is commonly used in the Direction Of Arrival (DOA) estimation. But when it realizes the direction finding, the long and short baselines in the array lead to the problems of baseline symmetry and phase ambiguity. An improved correlation interferometer algorithm based on quadrant classification is proposed. First, the time difference of signals arriving at each element is converted into phase difference, as well as the obtained phase difference is compared with 360°, and the obtained integer and remainder are recorded. Then the remainder is quadrant classified, after which the initial estimated value of the signal is obtained by using a traditional correlation interferometer algorithm. Finally, the final estimate value of the signal is calculated based on the inverse operation. Experimental simulations show that the improved algorithm successfully solves the problems of baseline mirror symmetry and phase ambiguity. Moreover, the accuracy of signal estimation is improved, the computational complexity is reduced, and the real-time performance of direction finding is improved. Therefore, it has significant value in the DOA estimation.