One important parameter in estimating the uncertainty of an atom gravimeter is the equivalent height due to the presence of non-negligible vertical gravity gradient. In this article, we report a novel method to determine the equivalent height based on the location-dependent Rabi frequency produced by modulating Raman lasers. We theoretically investigate this method and apply it on an atom gravimeter. Experimental results reveal that with this new method, 0.06 $\mu$ Gal uncertainty in gravitational acceleration can be achieved when taking the measurement uncertainty of the equivalent height ( $0.26247~\pm ~0.00021$ m) as the only contribution. This uncertainty is negligible compared with the current state-of-the-art gravity measurement uncertainty of 2–5 $\mu$ Gal. The demonstrated method can be widely applicable in most of the existing atom gravimeters for the evaluation of their equivalent height, especially those for high-precision metrology and fundamental physics test.