NFTs (Non-Fungible Tokens) have seen significant growth since they first captured public attention in 2021. However, the NFT market is plagued by fake transactions and economic bubbles, e.g., NFT wash trading. Wash trading typically refers to a transaction involving the same person or two colluding individuals, and has become a major threat to the NFT ecosystem. Previous studies only detect NFT wash trading from the financial aspect, while the real-world wash trading cases are much more complicated (e.g., not aiming at inflating the market value). There is still a lack of multi-dimension analysis to better understand NFT wash trading. Therefore, we present the most comprehensive study of NFT wash trading, analyzing 8,717,031 transfer events and 3,830,141 sale events from 2,701,883 NFTs. We first optimize the dataset collected via the OpenSea API. Next, we identify three types of NFT wash trading and propose identification algorithms. Our experimental results reveal 824 transfer events and 5,330 sale events (accounting for a total of \$8,857,070.41) and 370 address pairs related to NFT wash trading behaviors, causing a minimum loss of \$3,965,247.13. Furthermore, we provide insights from six aspects, i.e., marketplace design, profitability, NFT project design, payment token, user behavior, and NFT ecosystem

翻译：NFT（非同质化代币）自2021年首次引起公众关注以来经历了显著增长。然而，NFT市场充斥着虚假交易和经济泡沫，例如NFT清洗交易。清洗交易通常指同一人或两个合谋者之间的交易，已成为NFT生态系统的主要威胁。现有研究仅从金融层面检测NFT清洗交易，而现实中的清洗交易案例更为复杂（例如并非以抬高市场价值为目的）。目前仍缺乏多维度分析以深入理解NFT清洗交易。为此，我们提出了目前最全面的NFT清洗交易研究，分析了2,701,883个NFT中的8,717,031次转移事件和3,830,141次销售事件。我们首先优化通过OpenSea API收集的数据集，其次识别三种NFT清洗交易类型并提出识别算法。实验结果显示，与NFT清洗交易行为相关的有824次转移事件、5,330次销售事件（涉及总额8,857,070.41美元）及370个地址对，导致至少3,965,247.13美元的损失。此外，我们基于市场设计、盈利性、NFT项目设计、支付代币、用户行为和NFT生态系统六个维度提供了洞察分析。