On May 13th, Longhash published a paper to analyze the tracking error of the stable currency, and used the quantitative index of the index fund ETF, tracking error, to measure the stability of the value of the stable currency. The report selects the price data of USDT, DAI, USDC, TUSD, PAX and GUSD six stable coins for nearly 12 months from the CoinMarketCap website, and calculates the 30-day dynamic tracking error. The results show that the USDT market is much larger than other stable currencies, with moderate tracking error and occasional price fluctuations. The PAX market is medium in scale and the tracking error is very good. The USDC and TUSD markets are medium in scale and the tracking error is average; DAI, The GUSD market is small and the tracking error is poor.