Now that in language with garbage collection (GC) mechanism such as Java, the GC should be a direct impact on the performance of the program, and the requirement of real time GC is even higher in a real-time system. We proposed a memory reclamation scheme based on semi-space GC to satisfy the demands of real-time system. In the semi space copying collection process, large number of memory copying operations will bring a significant time overhead. Therefore, a mechanism of object classification and incomplete copying was proposed to reduce the costs of memory copying as well as to maintain a low degree of memory fragmentation. We implemented our solution on the Apache Harmony platform and the effectiveness of our collector prototype was measured through a series of benchmark tests.