In this paper, we introduce a new approach based on DC (Difference of Convex functions) Programming and DCA (DC Algorithm) for minimizing the maintenance cost involving flow-time and tardiness penalties by optimal scheduling and real-time assignment of preventive maintenance jobs on parallel processors. The main idea is to divide the horizon considered into H intervals. The problem is first formulated as a mixed integer linear problem (MILP) and then reformulated as a DC program. A solution method based on DCA is used to solve the resulting problem. The efficiency of DCA is compared with the algorithm based on the new flow-time and tardiness rule (FTR) given in [1]. The computational results on several test problems show that the solutions provided by DCA are better.