Reducing the execution time of program is a main goal of parallel processing, while an efficient task allocation algorithm is a crucial step, especially on NOW (network of workstations). In this paper, the problem of task scheduling in structural parallel control mechanism on heterogeneous net of workstations is studied. Based on principles of greedy algorithm, granularity controlling and feeding-back-liked assignment, an algorithm on scheduling tasks is put forward under structural parallel mechanism: SSA (sub-optimal scheduling algorithm). The exper-imental results show that it can get better performance than other algorithms on heterogeneous NOW.