As an important cornerstone of future digital civilization, smart contracts are being increasingly used in blockchain finance in innovative practice, and whether smart contracts have legal effect has become a question that academia must answer. This paper discusses the legal impact and application of smart contracts under the contract layer in the blockchain architecture, with a vision of an administrative legal system. Based on the operation principle of smart contracts, a method for detecting smart contract vulnerabilities that combines Glove word embedding and the Shapelet-Transform algorithm is proposed to improve data security during the fulfillment process. Finally, the smart contract model constructed in this paper is applied to the supply chain of agricultural products, and the legal effects of the smart contract are analyzed using practical examples. The transaction volume of unqualified agricultural products decreased from 19.4545 to 13.4655, which is lower than the production volume. The credit index of the smart contract model has increased, resulting in a shortened node performance time from 0.25s to 0.2s.