There is a problem of low positioning accuracy when using Apriltags to measure tags in long distance. In this paper, we analyze the causes of the problem, and propose a method to improve the longitudinal measurement accuracy and range of Apriltags based on relative positioning technology. This method solves the problem by dividing long distance into few short distance and obtains the space position by calculating with ensuring the measurement accuracy. When both direct measurement and indirect measurement results exist, combine the respective advantages of the two methods through the way of data fusion. This method can effectively improve the longitudinal distance measurement accuracy of tags at medium and long distances while ensuring the measurement accuracy of transverse distance and height. We verified the effectiveness of the method by conducting the simulation experiments and real experiments, achieved the reduction of 1 dm absolute measurement error and 0. 45% relative measurement error at a distance of 3 m ( equal to 12. 5 times the tag size).