Abstract -- This project collects various initiation models of debris flow caused by rains, compares the differences among the models, discusses the suitability of models, and then proposes an improved model for the use of debris-flow occurrence warning. The common rainfall parameters used in rainfall R and previous accumulated rainfall P. Based on the four rainfall parameters, debris-flow occurrence warning models debris-flow warning models are rainfall intensity I, rainfall duration T, accumulated could be classified into five categories: I-R model, I-T model, R-T model, I-P model and others. It has been found that there is inconsistent in defining a rainfall event used to analyze debris-flow initiation. There are about four difference definitions of a rainfall event used by previous debris-flow investigators. The four kinds of rainfall-event definitions have been applied to analyze the rainfall parameters. The results show that different rainfall-event definitions would result different rainfall parameters, and their differences are very large. The project proposed another two methods to define a rainfall event that would be suitable for analyzing debris-flow initiation. The rainfall parameters obtained by the proposed method are also compared with that obtained by the present method used by the Soil and Water Conservation Bureau (SWCB), Council of Agriculture. It is also found that the total accumulated rainfall calculated by days is close to that obtained by the present proposed two methods and by the SWCB method. This project also proposes a probability-based debris flow rainfall warning model that would be very useful in drawing warning levels of debris flow occurrence.