Aimed at the problem that the smoothing accuracy of Hatch filter in single frequency GBAS (ground based augmentation system) is reduced by the ionospheric anomaly, the influence of ionospheric delay on the smoothing accuracy of Hatch filter was analyzed systematically, and an improved adaptive Hatch filter algorithm was proposed. The code-carrier divergence was calculated according to the satellite signal, and its high frequency was suppressed by using the second-order linear time-invariant filter to detect whether the ionosphere is abnormal. A function model between the root mean square of smoothed pseudorange error and the ionospheric delay rate, the standard deviation of pseudorange measurement noise and the smoothing time was established, from which the optimal smoothing time of Hatch filter was determined. The verification experiments were carried out by using GBAS prototype developed in the laboratory. The experimental results show that the adaptive Hatch filter algorithm is able to calculate the optimal smoothing time according to the ionospheric delay rate of satellite signal. When the ionospheric is abnormal, the maximum airborne position error is reduced from 1.15 m to 0.43 m, which verifies the effectiveness of the proposed algorithm.