Concerning the problem that the traditional access control methods face single point of failure and fail to provide trusted， secure and dynamic access management， a new access control model based on blockchain and smart contract for Wireless Sensor Network （WSN） was proposed to solve the problems of access dynamics and low level of intelligence of existing blockchain-based access control methods. Firstly， a new access control architecture based on blockchain was proposed to reduce the network computing overhead. Secondly， a multi-level smart contract system including Agent Contract （AC）， Authority Management Contract （AMC） and Access Control Contract （ACC） was built， thereby realizing the trusted and dynamic access management of WSN. Finally， the dynamic access generation algorithm based on Radial Basis Function （RBF） neural network was adopted， and access policy was combined to generate the credit score threshold of access node to realize the intelligent， dynamic access control management for the large number of sensors in WSN. Experimental results verify the availability， security and effectiveness of the proposed model in WSN secure access control applications.