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Abstract: Stock market volatility risk is one of the most closely monitored risks, and forward-looking prediction of volatility risk carries significant theoretical and practical importance. Option market ambiguity is an indicator extracted from option prices that reflects the uncertainty in the probability distribution of the underlying asset's future returns, and its distribution pattern across different maturities constitutes the term structure of option market ambiguity. Based on data from SSE 50 ETF options, this paper constructs a slope indicator for the term structure of option market ambiguity—defined as the difference between long-term and short-term option market ambiguity—and finds that this slope indicator can effectively predict the one-month-ahead volatility risk of the SSE 50 ETF, as evidenced by lower mean squared prediction errors and out-of-sample R² values significantly greater than zero. The underlying mechanism is that changes in short-term option market ambiguity relative to long-term ambiguity reflect shifts in investors' perceived uncertainty regarding the short-term return distribution of the stock market, which in turn alter investors' trading willingness and trading behavior, affect stock market trading activity, and ultimately change the stock market's future short-term volatility risk. Further analysis reveals that the slope indicator of the option market ambiguity term structure exhibits strong robustness: it retains its predictive power for the stock market's future short-term volatility risk even after replacing the term structure estimation method, altering the volatility risk prediction horizon, distinguishing between upside and downside volatility risk, and controlling for underlying asset illiquidity and realized ambiguity. Moreover, the predictive performance of the ambiguity term structure slope indicator is stronger for high volatility than for low volatility, because when the level of stock market uncertainty is higher, investors find it more difficult to form clear judgments about future return distributions, and the ambiguity term structure slope thus conveys more information about future volatility. This paper offers insights for enhancing the precision of financial risk identification and safeguarding the stable operation of financial markets.