Stress has been shown to influence working memory (WM). However, little is known about the effects of acute stress on pilots’ WM with varying WM loads. The current study aims to shed more light on this issue. Forty-two pilots were randomly assigned to the stress or the control group. The stress group experienced acute stress induced by the modified Trier Social Stress Test (TSST), and the control group did not receive any stress induction. Then, all participants performed N-back tasks under varying levels of WM load (0-back, 1-back, and 2-back) to examine their WM. We measured their State-Trait Anxiety Inventory scores and salivary cortisol concentrations repeatedly throughout the experiment to determine the effects of induced stress. The results showed that (1) the modified TSST effectively induced acute stress in the stress group; (2) as the WM load level increased, the reaction time increased, and the accuracy decreased; and (3) there were no significant differences in reaction time between the two groups at different WM load conditions. However, there was an interaction effect for accuracy, which showed that the accuracy of the stress group was higher than that of the control group at the medium WM load (1-back). These findings suggest that acute stress improves pilots’ WM accuracy during moderately difficult tasks. The results of this study provide a theoretical basis for improving stress management and training pilots’ WM abilities.