Aiming at the influence of deviations in the beacon antenna rotating frequency on accuracy of TACAN signal azimuth estimation, analysis is made to the difficulty of estimating TACAN antenna frequency deviation in frequency domain at first. Then, a method is proposed which can enhance the practicability of existing TACAN antenna frequency estimation algorithm. Finally, a TACAN antenna frequency estimation algorithm based on Gauss-Newton iteration is proposed from the view of time domain, and the method for selecting the initial value of iteration is given, which can guarantee the convergence of the algorithm. This algorithm can realize the real-time estimation of frequency deviation. The simulation results show that the algorithm has high estimation precision and can be used for real-time monitoring of TACAN antenna frequency deviation.