Rapid access (RA) is an effective heuristic method for solving the permutation flow shop problem with the objective of makespan. This paper proposes a heuristic IRA (i.e., improved RA) for the two-stage flexible flow shop scheduling problem with head group constraint. In the heuristic IRA, two dispatch rules, i.e., earliest completion time first (ECT)) and earliest start time first (EST), are proposed for allocating devices for tasks. Benchmark testing results show that using ECT dispatch rule can significantly improve the performance of heuristic IRA. As comparison, the heuristic CDS and heuristic Palmer have also simulated under the same conditions, and the results show that the IRA is able to provide much better performance.