Monte-Carlo simulation of random lasing under diffusive regime of light propagation in active random medium was
carried out. Computing has been carried out for active media being suspension of dielectric particles in rhodamine 6G
solution. Dependence of emitted photons density distribution in active media, their total quantity and spectrum on active
medium length in a pump beam direction. Spatial distributions of pump radiation and amplification in a sample have
been taken into account. It has been shown that quantity of emitted photons non-steadily depends on sample length and
the maximal density of emitted photons is located at a depth near front (pump) sample side. Optimal active medium
length is exists and maximizes total number of emitted photons and narrows spectrum of emission. Computing results
are conformed to experiments.