The rapid development of the digital economy has profoundly influenced investor trading behavior and stock price volatility. This study constructs an investor sentiment index based on stock forum posts from Eastmoney Guba and examines how investor sentiment moderates the price responses of individual stocks to news events. Empirical results show that stock price movements following news releases exhibit sentiment-dependent patterns: under optimistic sentiment, stock prices tend to overreact (rise first and fall later), while under pessimistic sentiment, prices tend to drift downward. Portfolio analysis confirms the existence of sentiment-driven mispricing: the annualized excess return of the “pessimistic sentiment & positive news” portfolio over the “optimistic sentiment & negative news” portfolio reaches 6.8% after deducting short-selling costs. Furthermore, order imbalance is identified as a key transmission channel through which investor sentiment affects post-news price responses. The sensitivity of order imbalance to investor sentiment is significantly greater than to news tone. In over 47% of the cases (conservatively estimated), the direction of order imbalance is driven by sentiment, while news tone only affects its magnitude. These findings are robust across various specifications and provide new empirical evidence on sentiment-driven market behavior in China, offering important insights into asset pricing mechanisms in the digital economy era.