Abstract: In view of the problems that existing underground positioning algorithm based on UWB is complex and solution value is not global optimal, an improved trilateral positioning algorithm based on UWB was proposed. The algorithm is based on DW1000 chip and trilateral positioning algorithm, adopts bilateral two-way ranging method. Optimization objective function is set by solving the optimal solution of binary quadratic equation, and coordinate is two-dimensional, so as to reduce complexity of the algorithm. The invalid data generated in measurement process were screened out, effective search area is determined, and global traversal is conducted in the effective area to find global optimal positioning coordinates, which solves the problem that solution value is not global optimal. At the same time, in order to further improve positioning accuracy, appropriate measures are taken to increase the number of reference measurement nodes. The experimental results show that the average error of the proposed positioning algorithm is lower than that of the weighted trilateral positioning algorithm and the Taylor algorithm, and the positioning accuracy is improved obviously. Meanwhile, the algorithm has strong practicability, and measurement accuracy can be effectively improved by increasing the number of reference nodes.