The calculation of the travel time in 3-D velocity structure has been given in this paper.In the process of the genetic algorithms,considering large parameter space in the initial iterations and small parameter space in the final iterations,authors give mutation probability which is a large value in the initial iterations and small value in the final iterations.The formation of the mutation probability is linear and exponential with iteration.It is found that the exponential function is a more effective method.Using the exponentially reduced mutation probability,the hypocenter is obtained through genetic algorithms.The residual of the hypocenter is very small.