Abstract: Recall and precision are the basic criteria for evaluation of retrieval quality in information retrieval systems. Much effort and research has been done to solve the problem of the evaluation. Many methods have been proposed for evaluation of retrieval quality. However, they only reflect the average performance of retrieval but lack the analysis of stability of retrieval. In this paper, a new measure for evaluation of information retrieval quality is brought forward. The measure is based on some concepts that are called recall expectation, recall K variance, precision expectation, and precision K variance. Compared with other evaluation models of retrieval quality, this measure can reflect both the average performance and the stabilization of retrieval. Therefore, this model is better for evaluating the retrieval quality of information retrieval systems.