Based on the Quantile Regression Theory, a time-varying conditional expected loss model(?CoES) was constructed to measure the tail risk spillover of China''s A share core assets stock prices from April 2020 to March 2021, and to analyze the impact of core assets’price falling on the whole market. The empirical research shows that the greater the tail risk of the core assets index, the greater the risk spillover to the SSE Composite Index in extreme cases, and the two have a significant positive correlation. During the April 2020 - March 2021, when the market declines, the tail risk spillover of core assets to the market was higher than that of the CSI 500 during the same period. Among core assets, the healthcare sector is the most volatile and generates the highest spillovers, followed by the consumer sector, these two sectors have contributed the most to the market''s decline over the past year.