Returning straw to field is an effective way and realistic choice to promote the large-scale centralized utilization of straw. While an obstacle to the extension of straw return technology is the paradox between farmers'' willingness and their behaviors. As rational people, whether to return straw is a rational decision for farmers after weighing in family endowment. Besides, ecological cognition can also moderate the transformation between farmers'' willingness and their behaviors. These results in the contradiction between farmers'' willingness and behaviors. Based on the perspective of family endowment and the rural household survey in Hubei, Anhui and Hebei Province in 2017-2018, this paper analyzed the reasons for the paradox and tested the moderating effect of ecological cognition. Results show that: 1) there is a significant paradox between farmers'' willingness and behaviors of straw return. 85.5% of the farmers are willing to return straw while only 58.2% of the farmers actually did it; 2) the improvement of family endowment can restrain the paradox; 3) ecological cognition has moderating effect in the transformation between farmers'' willingness and their behaviors. Farmers with high ecological cognition have more consciousness and abilities to promote the willingness to adopt straw return practice than those with low ecological cognition; and 4) different types of farmers have different characteristics of paradox. Farmers who have received more help and with large-scale operations are less likely to behave the paradox.