Engineering mapping can not only assist engineers to find scheduling and quality problems, but also provide data basis to conduct further engineering analysis. Compared with traditional engineering surveying and mapping technology, UAV low altitude photogrammetry technology has the advantages of simple operation, good economy, and strong mobility. Accordingly, in this paper, UAV photography technology is being introduced into civil engineering, and the issue of its route planning is being discussed to achieve the three-dimensional real scene modeling of the site. In terms of the modelling problems, this paper divides the original site into proper zones and simplifies the route planning problem to a full coverage path planning problem under the irregular field, where obstacle avoidance planning does not need to be considered. Methodologically, the combination of A^*Algorithm and BINN algorithm have solved the problem of "dead zone" in BINN algorithm, and the setting of constraint rules has solved the problem of random walk in the initial stage of the algorithm.Finally, by taking an actual earthwork project as an example, the feasibility of the improved algorithm is being proved.