Abstract: The runoff study by using of simulated rainfall can significantly shorten the experiment period, and speed up the research process for the principles of rainwater infiltration and soil erosion. Currently, most rainfall simulators, which are bulky, complicated, expensive, and difficult to be adopted widely. A portable rainfall simulator consisted of the sprinkling system and the water supply system was designed to sovle above mentioned problems. This simulator employs a structure with single downward-oriented nozzles to realize a rainfall simulation, and it can artificially simulate different rainfall intensities as well as different rainfall durations by controlling the pressure of supplied water, and by changing the nozzle type. According to the rainfall properties test, this simulator realized simulated rainfall intensity ranging from 0 to 140 mm/h and rainfall uniformity over 80%. The raindrop diameter mainly distributed within the range 0.1-5.5 mm, and the raindrop speed at reaching ground ranging from 2 to 2.9 m/s was realized for different raindrop diameters. The test results were very similar with natural rainfall .The simulator can therefore effectively realize rainfall simulation.