Strengthening the publicity of agricultural insurance policy and catering for the internal needs of farmers are the first means to promote the purchase of agricultural insurance by farmers. Based on 985 micro survey data of farmers in Hunan， Hubei and Henan provinces， combined with the "self-interaction" theory and convergence psychology in communication science， this paper constructs a three-stage least squares method （3SLS） system estimation simultaneous equation to investigate the internal mechanism of farmers' purchasing agricultural insurance under the policy dissemination. The results show that the policy publicity will have a positive effect on the agricultural insurance purchase by improving the farmers' internal agricultural insurance awareness and the external public opinion perception. Comparing the two paths of action， the impact of policy awareness is more significant. Furthermore， with the increase of age and income，farmers' agricultural insurance purchase decision will be more influenced by internal policy awareness than external public opinion awareness， while the increase of education level will make the role of policy awareness more significant. Therefore， the relevant government departments should strengthen the publicity of information regarding agricultural insurance policy， pay attention to the internal demand of farmers for agricultural insurance， and create a favorable public opinion environment for insurance.