Making choice is self-control act and all acts of self-control are effortful and draw on a limited resource, resulting in a state that refers to as ego-depletion. The strength model of self-control provided a new perspective for discussing people’s choices. Studies have found that making choices would deplete self-control resource and lead to ego depletion. But we also poorly understood the reason why making choice have depletion effect. In this study we explored the reason of the choice depletion by setting and manipulating the variable of trade-off conflict difficulty and processing difficulty. Because trait self-control has robust influence on self-control behavior, we exercised strict control over subjects' trait self-control before first stage task. Trade-off conflict resolving should require self-control resources because which is most closely linked to executive function. Difficulty in information processing can make a choice seem difficult, but such difficulty may not draw much on executive resources. At the same time, ego depletion occurs mainly in series complex cognitive activity such as logical reasoning and problem solving which need executive control to transform information from a given state into other states. Reading choosing task and processing of option should not need information state transitions, so this two kinds of information processing difficulty should not induce ego depletion. Our hypothesis, therefore, is that the cause of depletion effect is trade-off conflict difficulty but not information processing difficulty. Self-control resources depletion was manipulated by Stroop task, which had been consistently proved to be effectively, distinguish high and low self-control resources. In experiment 1, participants were asked to finish trait self-control scale at first, then they were assigned to conditions in a 2 (trade-off conflict difficulty: high or low) × 2 (reading difficulty of select task: difficult or easy) between-participants design, afterwards, all participants fulfilled Stroop task. In experiment 2, before fulfilling Stroop task, participants were assigned to conditions in a 2 (trade-off conflict difficulty: choose for self or choose for other) × 2 (option information processing difficulty: 4 options or 3 options) between-participants design according to their scores of trait self-control. In both experiments, between the first and the second phase task, participants' moods were measured. The results showed that subjects' performance of Stroop task after making high trade-off conflict was significant lower than the subjects who made low trade-off conflict, reading difficulty of select task had no influence on Stroop task performance (experiment 1); Subjects' performance of Stroop task after making choices for themselves option information was significant lower than the subjects who made choices for others, number of options had no influence on Stroop task performance (experiment 2). In two experiments, the differences of Stroop task which various groups showed were not due to subjects' moods. Our findings also showed that resolution of trade-off conflict is a primary source of depletion but not information processing difficulty of choice. Future research need to reveal the function of other choice difficulties and further confirm the reason of the choice depletion.