This paper proposes a parallel processing system - Harray-for scientific computations. Data flow computers are expected to obtain the high performance because they can extract parallelism fully from a program. However, they have many problems, such as the difficulty of controlling the sequence of execution. The - Harray - system is an array processor which adapts two levels of control mechanism; data flow execution in each processor and control flow between processors, in order to take full advantage of both mechanisms. A task which is assigned to a processor is called a "macro-block". Three types of macro-blocking and three types of activation schemes for the macro-block which initiates its execution are introduced in order to attain the high performance. Moreover, a hardware synchronization mechanism is used to reduce synchronization overhead and to gain the liner speedup of the - Harray - system. In this paper, the system architecture of the - Harray - system and its performance evaluation by software simulation are presented.