The smart contract is a decentralized application widely deployed on the blockchain platform, e.g., Ethereum. Due to the economic attributes, the vulnerabilities in smart contracts can potentially cause huge financial losses and destroy the stable ecology of Ethereum. Thus, it is crucial to detect the vulnerabilities in smart contracts before they are deployed to Ethereum. The existing smart contract vulnerability detection methods (e.g., Oyente and Secure) are mostly based on heuristic algorithms. The reusability of these methods is weak in different application scenarios. In addition, they are time-consuming and with low accuracy. In order to improve the effectiveness of vulnerability detection, this study proposes Scruple: a smart contract timestamp vulnerability detection approach based on learning data-flow path. It first obtains all possible propagation chains of timestamp vulnerabilities, then refines the propagation chains, uses a graph pre-training model to learn the relationship in the propagation chains, and finally detects whether a smart contract has timestamp vulnerabilities using the learned model. Compared with the existing detection methods, Scruple has a stronger vulnerability capture ability and generalization ability. Meanwhile, learning the propagation chain is not only well-directed but also can avoid an unnecessarily deep hierarchy of programs for the convergence of vulnerabilities. To verify the effectiveness of Scruple, this study uses real-world distinct smart contracts to compare Scruple with 13 state-of-the-art smart contract vulnerability detection methods. The experimental results show that Scruple can achieve 96% accuracy, 90% recall, and 93% F1-score in detecting timestamp vulnerabilities. In other words, the average improvement of Scruple over 13 methods using the three metrics is 59%, 46%, and 57% respectively. It means that Scruple has substantially improved in detecting timestamp vulnerabilities.