We proposed a strategy to improve the item-selection strategy in knowledge structure-based adaptive testing system(KSAT) in order to reduce guessing effects. Thus we proceeded simulate experimentation in KSAT to evaluate the efficiency of improved item-selection strategy. KSAT is an adaptive testing system based on knowledge structure which not only decrease the test items but also preserve prediction accuracy. However, the prediction accuracy in KSAT will be affected by guessing items of upper-level concept . According to results of simulate experimentation, the improved strategy can decrease the test items and preserve prediction accuracy.