Aiming at the problem of current scheduling algorithm for multi-core which fails to consider that the nodes on the critical path have a major impact on the ending time of tasks, leading to the delay of the task completion time; a scheduling algorithm based on critical path and task duplication (CPTD) is proposed. Firstly, the fork-nodes were duplicated to change the task graph into products processing tree, then the critical path in the processing tree were found, and the father nodes of the nodes on critical path were made to work at the earliest time. These operations can advance the start time of nodes on critical path. The purpose of the above operation is to shorten the implementation of the mandate of the total time. Theoretical analysis shows that the algorithm can achieve a single task fully parallel processing on multi-core, and also can shorten the completion time of the tasks.