Traditional approaches to simultaneous localization and mapping (SLAM) are unable to extract semantic information from the scene or meet the high-level task requirements of robots, and the efficiency of 3D map construction is low. To solve this problem, a 3D semantic map construction system is proposed in the paper to build a 3D semantic map. Firstly, the current position of the camera is estimated and optimized based on ORB-SLAM algorithm, and the globally consistent trajectory and pose are obtained. Then the semantic segmentation network is designed to predict semantic category of every pixel. The 3D semantic point cloud information is generated by combing the semantic information and the object point cloud. The global consistent camera pose estimated by visual SLAM algorithm is integrated with the semantic point cloud information to generate a 3D semantic map. Finally, we use an Octomap which is applied to navigation projects for map storage to reduce the storage capacity of the map. The experimental result verifies the accuracy and efficiency of this method.