Solution of radiative intensity plays an important role in many areas, such as combustion monitoring, fire detection, and infrared imaging simulation, etc. The reverse Monte-Carlo method is a widely used method due to its high accuracy and flexibility. However, it has not been applied to solve radiative intensity in systems discretized by unstructured grids which are usually applied in complex geometries. This brings difficulty if the solution of radiative intensity is applied to practical radiative systems of irregular geometries, especially coupled with other physical problems, such as fluid-flow, etc. In this work, the reverse Monte-Carlo method based on unstructured grids is developed for solving radiative intensity in participating media with complex geometries. In order to improve the efficiency of ray tracing process, a preprocessing procedure is introduced to establish topological relationships between unstructured grids. Radiative heat flux and radiative intensity in radiative systems with different geometries of a cube and a triangular prism are calculated. Comparing with results of other methods in literatures, radiative heat flux and radiative intensity calculated by the present method shows very good accuracy.