An improved preconditioned conjugate gradient squared (PCGS) algorithm has recently been proposed. This algorithm is more accurate and efficient than the conventional PCGS algorithm, and retains the advantages of the left-PCGS in terms of a solution structure. In this paper, we propose a changing over stopping criterion for the improved PCGS, that results in a higher accuracy than the conventional and the left-PCGS. A series of numerical results illustrate the stable solving statuses and the enhanced effectiveness of the improved PCGS with changing over stopping criterion.