Indoor propagation models attract much interest these days because of their importance in the applications of 3G/4G network planning and optimisation. The accuracy and running speed directly affects the practical use of such models. This paper extends a discrete ray launching model IRLA (Intelligent Ray Launching Algorithm) to indoor scenarios. A typical office room will be selected to validate this model. The efficiency and suitability of IRLA for indoor scenarios will be investigated and comparison with two referenced indoor models are given. The comparisons show that the modified IRLA for indoor scenarios obtains high accuracy within a reasonable time scale. It is promising because it is uniquely efficient on computation of rays, which outperforms most of the propagation models.