The knowledge of rainfall in terms of its intensity, duration, frequency, temporal distribution and droplet size distribution are important for appropriate estimation of runoff and erosion. That is required for hydrologic design of soil and water conservation structures. However the rainfall is the natural process and governed by the random processes. It takes several years to cover the entire range of above stated parameters and to study their effects on runoff and erosion. Therefore for quick understanding of this process and to accelerate the part of research on this aspect, it is necessary to observe the desired range of these parameters in the laboratory on controlled situation. Rainfall simulators they have the capability to vary the rainfall parameters in the desired range and therefore useful for such studies. Rainfall simulators offer the possibility of the advances in understanding the basic processes of runoff and erosion and the speed of the research is accelerated. One needs not to wait for the right kind of rains to come at right time for obtaining the results. The relationship developed include: water pressure, raindrop size and rainfall intensity with soil loss.