This study applies a phonological approach to word stress in Chinese Putonghua. Existing findings have shown that word stress in Putonghua is mostly unpredictable. None of the studies, whether based on intuition, acoustic experiments, or metrical and OT phonology, has reached a uniform model for Putonghua word stress.Through analysis of phonological theories and comparative studies of word stress in other languages, especially English, the author believes that the current phonological theory is well-equipped for the explanation of Putonghua word stress.The present study is an attempt to combine phonetic experiments and phonological explanation. Experiments are designed and implemented with care taken to avoid repeating the work of others. It is discovered that word stress is signaled by intensity (or energy).Further investigation in the research found that the word stress in Putonghua and that in English belong to different concepts. In Putonghua, word stress means relatively more weight on tonal syllables and has no relation with the toneless syllable, which, weak by origin, does not participate in foot construction and can be considered to be "extrametrical" to the syllable on its left that must be stressed to form a disyllabic iambic foot with the syllable on its own left.On this basis, the present work found the algorithm* and constraint ranking** for Putonghua word stress. It is found that Putonghua word stress has the following regularities:1) Tonal syllables form iambic feet.2) The toneless syllable is extrametrical to the tonal syllable on its left.3) Foot construction can cross word boundaries.4) Logical stress or syllables with long vowels can be lengthened to form a foot of its own, which is naturally stressed.5) In expanded strings of words, some stresses are stronger than others, thanks toextralinguistic factors like logic, emphasis, or emotions. It is therefore a matter of modes of speech rather than linguistic rules and, as a result, the positions and occurrences are unstable.Because feet can be constructed across word boundaries, the stress rule outlined above reaches beyond stress on the word level, hence the rule for Putonghua stress in general.Notes:Putonghua stress algorithm Cyclic:Extrametricality Syllable lengthening Foot construction End Stress Line conflation Constraint ranking for Putonghua stress Parse-a , WSP , Iamb Nonfinality