Abstract: In traditional Gaussian beams tracing algorithms, a large number of beams need to be taken into consideration for accurate propagation loss prediction, which leads to high complexity and high computational consumption. An algorithm to speed up a beam tracing engine is described which allows to select arbitrary areas around transmitters and receivers combining with 3D mesh grid approach. By using a grid space division, the area selection is defined by the union of all voxels crossed by the straight lines linking the transmitter and each receiver. Then the BT engine will only search the rays which interact with facets contained in the selected area. The simulation results show that the precision of our method is almost the same as traditional beam tracing methods while the computation time is far less than the latter. The method is particularly suitable for evaluating propagation in urban scenarios where not all the objects are involved in the ray propagation between the transmitter and the receiver.