DAG task scheduling is the current hot topic. In task model of DAG, the order of task scheduling affect the service satisfaction of users on one hand, and also affect utilization rate of cloud service resources on the other hand. High efficient task scheduling algorithm may strengthen the resources distribution of the multi-core and the parallel computing ability. HEFT algorithm and CPOP algorithm are of lower efficiency in related task scheduling. Based on HEFT algorithm and CPOP algorithm, a dependent task scheduling model and task scheduling algorithm IHEFT (Improvement Heterogeneous Earliest Finish Time) algorithm are proposed in this study. The IHEFT algorithm mainly optimizes two aspects:task ordering and task scheduling. The variance of task scheduling cost on every processor core and the average communication overhead are the basis of task ordering. In the stage of task scheduling, task duplication of some nodes in DAG with some conditions can make full use of heterogeneous processor resources and shorten the completion time of task set. Experiment results show that the IHEFT algorithm performs more performance than the HEFT algorithm and the CPOP algorithm in terms of the task scheduling Makespan, the average waiting time and the average value of Slack.