Complex river engineering mapping is often affected by a variety of factors such as lush vegetation，weak signal link and mountain occlusion，which make it difficult to carry out traditional surveying and mapping means. Through the comparative study of UAV LiDAR and tilt photogrammetry in complex river engineering mapping，the complementary advantages and fusion methods between the two are found out. The experimental results show that the LiDAR data incorporating textured image information has accurate spatial geographic information and clear land boundary information.The detailed expression of the skew model corrected by LiDAR data is significantly improved，and the contour expression of the model is clear and manual interpretation is easier.The results effectively overcome the disadvantages of UAV single measurement technology and traditional measurement technology，and can quickly build a more accurate river digital twin model.