Objective Consultation length, the time spent between patient and health care provider during a visit, is an essential element in measuring quality of health care patients receive from a primary care facility. However, the linkage between consultation length and process quality and diagnosis quality of primary care is still uncertain. This study aims to examine the role consultation length plays in delivering process quality and diagnosis quality, two central components of overall primary care quality, in rural China. Methods We recruited unannounced standardized patients (SPs) to present classic symptoms of angina and tuberculosis in selected healthcare facilities in three provinces of China. The consultation length and primary care quality of SPs were measured and compared with both international and national standards of care. Ordinary Least Squares (OLS) regressions for process quality (continuous dependent variable) and Logistic regressions for diagnosis quality (binary dependent variable) were performed to investigate the relationship between consultation length and primary care quality. Results The average consultation lengths among patients with classic symptoms of angina and those with symptoms of tuberculosis were approximately 4.33~min and 6.28~min, respectively. Providers who spent more time with patients were significantly more likely to complete higher percentage of recommended checklist items of both questions and examinations for angina ($β~$=~1.39, 95%CI 1.01– 1.78) and tuberculosis ($β~$=~0.89, 95%CI 0.69– 1.08). Further, providers who spent more time with patients were more likely to make correct diagnosis for angina (marginal effect = 0.014, 95%CI 0.002– 0.026) and for tuberculosis (marginal effect = 0.013, 95%CI 0.005– 0.021). Conclusions The average consultation length is extremely short among primary care providers in rural China. The longer consultation leads to both better process and diagnosis quality of primary care. Practice Implications We recommend primary care providers to increase the length of their communication with patients. To do so, government should implement healthcare reforms to clarify the requirements of affordable and reliable consultation length in medical care services. Moreover, such an experience can also be extended to other developing countries.