The invention belongs to the field of cloud computing application, and relates to method for task rely relation description, decoupling, parallel scheduling and the like in cloud service. Rely task relations are provided, and a decoupling parallel scheduling method of rely tasks are constructed. The method comprises first decoupling the task rely relations with incoming degree being zero to construct a set of ready tasks and dynamically describing tasks capable of being scheduled parallelly at a moment; then scheduling the set of the ready tasks in distribution type and multi-target mode according to real time resource access so as to effectively improve schedule parallelism; and during the distribution of the tasks, further considering task execution and expenditure of communication (E/C) between the tasks to determine whether task copy is used to replace rely data transmission so as to reduce the expenditure of communication. The whole scheduling method can schedule a plurality of tasks in the set of the ready tasks in dynamic parallel mode, well considers performance indexes including real time performance, parallelism, expenditure of communication, loading balance performance and the like, and effectively improves integral performance of the system through the dynamic scheduling strategy.