In system-level synthesis, the allocation of resources is always decided by the designer or explored in the outer-most loop. In this paper, a heuristic scheduling algorithm is proposed to find the resource allocation during its running process. It determines the appropriate number of required resource instances based on the system partition in scheduling, and generates the corresponding resource allocation, scheduling and assignment solution. Such an algorithm can simplify the system-level design exploration to a procedure of system partitioning, scheduling and evaluation, and can improve the exploration efficiency. Experimental results show the feasibility and validity of the approach.