In recent years, commercial scandals have emerged in an endless stream and the universality and seriousness of corporate unethical behavior has become increasingly prominent. This has aroused widespread concern in various sectors of society. Hannah (2013) found that monitoring employees through accountability mechanisms could reduce their unethical behavior. However, different types of business scandals suggest that accountability could also have a malfunction. In order to better curb corporate unethical behavior, we must clarify the boundary conditions and causes of failure of accountability. We believe that in the face of accountability, individuals with promotion focus are more prone to unethical behavior in the state of self-depletion. This paper confirms these conjectures through one pre-experiment and two formal experiments. In the preliminary experiment, we recruited 30 undergraduate students to participate. We determined the appropriate number of questions in the formal experiment by using three sets of word confusion test tasks with different amounts of questions to ensure the reliability of the experimental materials. Experiment 1 was based on the pre-experimental materials and had 120 undergraduates who were randomly divided into four groups using a 2 (accountable/non-accountable) × 2 (promotion focus/prevention focus) inter-group experimental design. It is to examine the effect of the interaction between accountability and regulatory focus on unethical behavior. Participants can receive a reward of two Chinese Renminbi for each correct answer. If the participant takes more than they earned, it means that they have engaged in unethical behavior. Experiment 2 added the measurement of ego-depletion to examine the mediating effect of ego-depletion between accountability and unethical behavior under promotion focus. Meanwhile, we changed the manipulation method of adjustment orientation to examine the relationship between accountability, regulatory focus and unethical behavior. Through analyzing experimental data by SPSS 19.0, we have reached the following conclusions: (1) The relationship between accountability and unethical behavior was positive/negative under promotion/prevention focus. (2) The relationship between accountability and ego-depletion was positive under promotion focus. (3) Under promotion focus, accountability of individuals would increase their ego-depletion and therefore promote unethical behaviors; which meant ego-depletion played a mediation role in the relationship between accountability and unethical behavior. Different from the previous study of stable personality traits, such as Machiavellianism as a research variable (Greenbaum, Hill, Mawritz & Quade, 2017), we selected the variable regulatory focus, which is situational control in the process of exploring the relationship between accountability and unethical behavior. It is not only theoretically but also impractically meaningful. After we figured out the moderation role of regulatory focus and mediation role of ego-depletion, it helped us find a way to reduce the occurrence of unethical behavior that is to provide a less promotional focused environment. When the employee shows signs of fatigue, burnout, etc., superiors should supplement his psychological resources, such as proper rest. Afterwards, managers should reward employees who have achieved their goals through ethical measures.