Abstract: With the wide application of large mining trucks in open-pit mines in China,the establishment of an pit-middle bridge transportation system has gradually become an effective method of saving transportation costs. In order to give full play to the role of the pit-middle bridge transportation system in open-pit mines in saving transportation distance,the important parameter of the system-bridge deck height is optimized. This paper analyzes the change law of the truck transportation distance between the pit-middle bridge transportation system and the double-loop transportation system,takes the level of the pit as the benchmark,and considers the dynamic changes of the return distance from different levels to the bridge deck. According to the principle of minimum transportation power,the results of stripping materials at different working faces dynamic demarcation position,and on this basis,establish a calculation model of internal discharge transport work,and then obtain transportation costs. This model expands the service scope of the pit-middle bridge transportation system;in order to reduce the amount of secondary stripping of the bridge and realize the economical and reasonable removal of the bridge,the shape of the bridge at the overlapping position,the composition of the bridge and the secondary stripping process were analyzed,and an economically reasonable secondary was proposed. The concept and calculation method of stripping ratio,the ratio of the economically allowable maximum secondary stripping volume to the mining volume was obtained,so as to determine the maximum secondary stripping depth,and further establish the bridge demolition cost model;according to the principle of maximizing profit,the optimal height of the bridge body of the pit-middle bridge system is determined,so that the pit-middle bridge system of the near horizontal open pit mine can fully play its role and has certain universal value. Aiming at the current situation of Baorixile open-pit coal mining,it is found through model calculation that as the height of the bridge increases,the overall service range of the bridge increases,and the number of steps within the service range shows a law of changing from less to more to less;the transportation cost saved by a certain step decreases as the height difference between the step height and the bridge body increases;the maximum cost savings of different bridges increases with the increase of the height of the bridges. In the end,the best bridge height is 55 m,and the bridge can be increased by about 29.015 million yuan in one bypass cycle.