Life is filled with uncertainty that imposes challenges for goal-directed effort. For example, whether effort reaps reward impacts the effort process. Real-life activities involve a long-term input of effort, implying that our effort process should be stably and consistently managed. The present study investigated how efficacy modulates the effort process from the perspective of overall performance and effort stability. Using a mini-block Stroop task and electroencephalography, we manipulated performance-reward contingency to pinpoint behavioral and neural features at each time stage (preparation, execution, and feedback-processing). Our findings revealed an efficacy-modulated effort process from three aspects. First, high efficacy induced a more prepared state before target presentation, which was identified by two neural indicators: contingent negative variation (CNV) and β oscillation (13–20 Hz). Then, drift rate and decision boundary reflected how people executed the task under different efficacy levels. Moreover, CNV and β oscillation affected sustained effort by modulating the drift rate, indicating preparatory state changed the execution to influence sustained effort. Finally, feedback-P3b captured shifts in the sustained effort after receiving different feedback. Taken together, these findings showed that efficacy modulates effort at each time course. Informative signals about efficacy and feedback are beneficial to trigger high-quality preparation and execution and drive effort adjustment.