汉语的句末语气词具有表义功能又承载着语句调尾，其韵律特征的改变可能影响说话人的语气表达和听话人的语气识别。本研究以北京话句末语气词“吧”为例，通过对采集到的北京话语料进行声学分析，发现句末语气词影响语气表达的韵律因素主要是音长和音高，然而“半信半疑”的性质使得“吧”的韵律特征和表义功能不是简单的对应关系。然后通过听辨实验，验证了句末语气词韵律特征的改变的确会带来语气识别结果的变化：第一，对于同形的陈述句和疑问句，句末语气词“吧”的音长越短，句子被识别为陈述句的概率越大；第二，句末语气词“吧”的音长、音高和音强的增加，都会使听者感到祈使句履义语气增强；第三，句末语气词“吧”的音长延长、音高降低会使听者感觉发音人的非确认语气增强。最后，听辨实验结果显示，男性听话人受句末语气词韵律特征改变的影响更大，女性语音中的疑问语气、履义语气和非确定语气更容易被人识别，女性听话人识别句子功能语气、判断评判语气强弱的速度更快。

The sentence-final modal particles in Chinese have semantic functions and carry the tail of tone, whose prosodic features may affect the speaker’s expression and the listener’s recognition of mood and modality. Taking sentence-final modal particle ba in Beijing dialect as example, firstly, this study analyzed the prosodic features of ba in collected corpus and found that the duration and pitch of ba have key influences on mood expression. However, there does not exist a simple positive correlation between its prosodic features and its semantic functions. Secondly, it was verified by auditory discrimination experiments that the prosodic features of ba affect the recognition of the mood and modality. The shorter the duration of ba, the greater the probability of identifying the sentence with ba as a declarative sentence between homogeneous declarative sentences and interrogative sentences. The increase in duration, pitch and intensity of ba will make listeners suppose that the deontic modality becomes more forceful. The increase in duration and decrease in pitch of ba will make listeners feel that the epistemic modality becomes less assertive. Lastly, this study reveals that male listeners were more affected by the change in the prosodic features of the sentence-final modal particle ba, while the interrogative mood, deontic modality and less assertive epistemic modality in female speech are more easily to recognize, and that female listeners were faster at mood and modality recognition.