The speech intelligibility in rooms is evaluated using the room impulse responses obtained from the room acoustical simulation software ODEON. The simulated room impulse responses are first convolved with the speech intelligibility test signals recorded in an anechoic chamber, then reproduced through the earphone. The subjective Chinese speech intelligibility scores are obtained and the relationship between Chinese speech intelligibility scores and speech transmission index (STI) is built and validated. The result shows that there is high correlation between Chinese speech intelligibility scores and STI. The STI method can predict and evaluate the speech intelligibility for Mandarin Chinese without changes in the algorithm of the weighting values for diotic listening in rooms.