Improving the quality of agricultural products is the key factor in promoting agricultural development in the Belt and Road program. Although many studies have investigated the relationship between social capital and performance, the findings are inconsistent. Moreover, the mechanism of how social capital affects the quality performance of agricultural products remains unclear. Accordingly, this study developed a theoretical model with propositions from a social capital-quality performance of agricultural products paradigm for examining and comparing the three dimensions of social capital: The relationships among cognitive (measured by shared values), relational (measured by reciprocity) and structural (measured by communication), and their role in ensuring quality performance of agricultural products from the company and farmer perspectives. This study selected the companies and farmers in “A company + farmers” model. The data analysis is based on a sample of 184 companies and 414 farmers. The results show that shared values and communication have a significant positive effect on reciprocity. In terms of the influence on reciprocity, communication is higher than shared values from both the corporate and farmer perspectives. The three dimensions of social capital have different effects on quality performance of agricultural products. On the company side, communication and reciprocity in social capital have a significant positive effect on the quality performance of agricultural products, with the order of effect being communication first followed by reciprocity. On the farmer side, reciprocity and shared values have a significant positive effect on the quality performance of agricultural products, with the order of effect being reciprocity first followed by shared values. These findings have positive theoretical and practical significance for companies and farmers aiming to improve the quality of agricultural products.