Execution time is very important for job scheduling. In this paper, the execution characters of Hadoop MapReduce jobs are analyzed, and then a new method is proposed to compute the execution times of these jobs. The method takes the execution times of map task and reduce task as input data. It captures these execution times by pre-executing under an assumption. The method has been evaluated in a Linux cluster, the experiment results show that the method computed the execution times of jobs with the error ra...