A calculation method of complex tank capacity is proposed based on the laser point cloud and building information modeling (BIM) technology. The bulkheads and inner components are first segmented based on the three-dimensional (3D) point cloud data of complex tank. The 3D reconstruction is completed based on the point cloud data of bulkheads and inner components through the BIM technology. The real-time calculation of tank capacity in different attitudes is done through the 3D model of tank. The proposed method is evaluated through the point cloud data of a complex tank in Shanghai. The research results show that this method can be used to quickly and accurately acquire tank capacities in different attitudes with high reliability and high practical application value.