The computation effort of ray tracing with the shortest path method (SPM) is strongly dependent on the number of the discretized nodes in a model and the number of ray directions emanating from a secondary source node. In the traditional SPM, a secondary source emanates rays to all the surrounding nodes. Obviously, most of them are not minimal traveltime raypaths. As a result, the efficiency of SPM can be greatly improved if some measures are taken to avoid those unnecessary computations. In the current study, we apply the traveltime information of neighbouring nodes and the incident rays to determine the effective target propagation directions of secondary source nodes in 2D case. Generally, the effective propagation directions are narrow bands with few surrounding nodes. Thus, most unnecessary ray directions of secondary source nodes are avoided. 2D model tests show that the computational speed of the improved method is about several to tens of times of that of the traditional SPM with the increase of network nodes and cells.