The traditional triangle elevation method for ranging is affected by the error by vertical refraction of the atmosphere, distance measuring error and the error in measurement of the heights of the instrument and the targets, as a result, it is difficult to control the measurement accuracy and the working efficiency is low. To overcome these, this paper proposes a triangular elevation leveling method based on high and low prism method, that is, two high -precision total stations with automatic alignment functions are used to perform multiple measurement returns opposite observation in multiple periods of time on the self-designed high and low prism set. It is found after the cross-river measurement of the main body of Yanji Changjiang River Bridge in Hubei Province that, the maximum error of the height difference between measurement returns was 10.00 mm, and the maximum error of loop closure was 1.30 mm, and after adjustment, the accidental error per kilometer is only ±0.71 mm, the mean square error of elevation at the weakest point is ±0.20 mm, and the mean square error of elevation in the weakest survey section is ±0.20 mm, which all meet the limit requirements of the second-class leveling measurement. It has been proved that this method can meet the second-class leveling requirements for long-distance cross-river leveling of less than3500 m, and improve the working efficiency by 50% compared with the traditional ranging triangle elevation method, worth wide promotion and application. [ABSTRACT FROM AUTHOR]