Sliding window join aggregation continuous queries (J-A queries for short) are often used in data stream applications. The intuitive method for processing these queries is to construct steaming operator tree and execute the tree in pipeline. The space cost of this method is O(α×β) , where α and β are the sizes of two sliding windows respectively. To reduce the requirement of memory, which is the most expensive resource in data stream query processing system, two novel sliding window J-A continuous query processing algorithms IC and TC are presented in this paper, whose space cost are both O(α×β). Theoretical analysis and experimental results show that the algorithms are more effective.