It has been widely recognized that the amount of people infected with human immunodeficiency virus (HIV) has been increasing in recent years, especially in developing countries.The important characteristic of the threshold for a person is the time to attain the break down point. A person affected having three sources two Exponential and one Erlang distribution with independent thresholds is considered, the Expected time and variance of the time to cross the threshold are obtained using the shock model and cumulative damage process in the field of Stochastic Process.The assumptions made are somewhat artificial, but are made because of lack of detailed real-world information.To illustrate the method described in this paper, some limited simulation results are discussed. This Study will be Useful for Bio-Statistics research Scholar.