Cooperative support can improve the cognitive and behavioral abilities of smallholder farmers，and is an exogenous force affecting the quality control behavior of smallholder farmers. This paper tries to deconstruct the influence logic of cooperative support on the quality control behavior of small farmers from three aspects： strengthening cognition，improving willingness and reducing the deviation probability of willingness and behavior，and conducts an empirical test based on 419 micro research data in three counties of Dingxi City，Gansu Province. The study found that the cooperative support has significant positive influence on the reduction of fertilization and dosage application， adoption of soil testing technology and integrated pest control technology，and the conclusion still holds after robustness test； there are group differences and intergenerational differences in the influence of cooperative support on different dimensions of quality control behavior of small farmers. Further inspection found that cooperative support can influence the quality control behavior of small farmers through three intermediary channels： strengthening cognition，improving willingness and enhancing ability. Accordingly，this paper puts forward appropriate countermeasures and suggestions in three aspects： strengthening the autonomous mechanism of “cognition-willingness-behavior”，jointly building the high-quality development mechanism of cooperatives and establishing the interest connection mechanism between cooperatives and smallholder farmers.