Abstract: To solve the engineering problem of cumulative amplification of azimuth transmission errors and difficulty in guaranteeing horizontal breakthrough accuracy for short sides (≤200 m) in cross double traverse networks of long large-high-speed railway tunnels, technical practice of short-side azimuth transmission error control is carried out with the 8076m Fankuai Tunnel on the Chongqing-Yuxi High-speed Railway as the research object. Four core error sources, namely angle measurement error, centering error, lateral refraction error and vertical deflection error, are clarified through error tracing. A multi-source coupling error model is constructed based on the law of error propagation, and the error contribution weights of three short-side lengths (150 m, 180 m and 200 m) are quantified. Combined with the tunnel’s characteristics of large height difference (693 m) and complex geological conditions, a five-dimensional integrated accuracy improvement system is proposed, including forced centering, optimized gyro orientation, staggered network layout, quantitative lateral refraction correction and vertical deflection correction. Verified by comparative tests on three short-side sections and three months of stability monitoring, the mean square error of short-side azimuth transmission is reduced from 3.21″ to 0.58″, and the final horizontal breakthrough error of the tunnel is 38.7 mm, which meets the specification requirement that the horizontal breakthrough mean square error of 350 km/h high-speed railway tunnels is ≤150 mm. The practical results can provide technical reference for short-side traverse control measurement of similar long large-high-speed railway tunnels.