Abstract: The uniform cylindrical pulse source is often used as calibration source. Based on Monte Carlo techniques, the distribution of the irradiance at the output plane of the cylinder is simulated by variable weight method and fixed weight method. The distribution of the light is affected by the type of reflection, the position of the light source, and the shape of the cylinder. Simulation and experiment results show that, when light source located at the center of the cylinder with an aspect ratio of 3/2 (length to diameter), and was diffused by the cylinder inner surface in transmission, the required uniformity was achieved.