Rhythm affects the speech perception of events unfolding over time. However, it is not clear to what extent the rhythm could affect the processes of sentence speech production. In this event-related potential (ERP) study, we examined whether a particular rhythmic pattern could affect the planning of speech production before articulation. We recorded electrophysiological (EEG) and behavioural (reaction time) data while participants read aloud a target speech in Chinese. Target speeches were sentences or phrases consisting four characters, with regular (e.g., the 2 + 2 pattern; numbers in the brackets represent the number of syllables) or irregular (e.g., 1 + 3) rhythmic patterns, which were preceded by congruent or incongruent musical rhythmic patterns formed by simple pure tones with different temporal intervals. Behavioural and ERP findings indicated a rhythmic priming effect in comparing congruent and incongruent conditions in the regular target speeches, but not in the irregular ones. An early component (N100) that was elicited in response to target speeches that were rhythmically mismatched to primes was linked to the detection of hierarchical linguistic units, which did not conform to expectations. A later negative component (N400) was thought to reflect the violation of expectation on rhythmic pattern in speech production. These findings suggest that rhythmic pattern constrains grammatical and prosodic encoding during speech production, and support the hypothesis that speakers form a grammatical or a prosodic abstract frame before articulation.