The policy of voluntary certifications is implemented in Chinese agricultural market. We take the type of boundedly rational consumers into consideration and analyze how the proportion of boundedly rational consumers influences the effectiveness of the voluntary certification mechanisms with a duopoly game model between high-quality and low-quality firms. Results show that the change of the boundedly rational consumers proportion will lead to different certification behaviors and different market equilibrium. The existence of boundedly rational consumers is an important factor of the failure of voluntary certification mechanism. When the proportion is very high，the voluntary certification will not play an effective role in improving market efficiency.