The two-dimensional distribution of gas concentration field under different distributions of light path is simulated using the computer simulation technology, and the connection between the distribution of light path and the reconstruction accuracy is researched. Reconstruction accuracy in different distributions of light path is compared by calculating the normalized mean absolute distance criterion, and the light path distribution of better reconstruction accuracy is got. The results show that improving the utilization rate of laser path can enhance the reconstruction accuracy in the case of less light path. And the validity of results are verified by calculating the reconstruction accuracy of the optimized light path distribution.