Many real-time systems have hard deadline periodic tasks along with soft deadline aperiodic tasks. An algorithm to improve response time of soft aperiodic tasks is presented in this paper. Existing methods of scheduling both periodic and aperiodic tasks are all based on RM (rate monotonic) scheme. Among them, stealing slack time from periodic tasks has been proved to be an optimal method. However, the RM scheme limits the processor utilization, therefore limits the stealable time of periodic tasks. The potential processor utilization of the DD (deadline driven) scheme can reach 100%. The presented algorithm applies the DD scheme to periodic task scheduling as it needs, and shortens the response time of aperiodic tasks. The experimental results show that the new algorithm provides performance higher than all existing algorithms, and the increased run-time overhead is not very high.