According to the self-determination theory of academic motivation (SDT), three basic psychological needs—autonomy, competence, and relatedness—significantly impact a person’s degree of motivation, including amotivation, extrinsic motivation and intrinsic motivation. Academic motivation strongly correlates with essential measures of academic achievement and well-being outcomes. There is, however, a paucity of data indicating possible variations in academic motivation among various groups, particularly among students from multiple cultural origins. This study used a sample of 588 secondary school students from Chinese Dai and Han ethnic backgrounds to explore the possible cultural differences in academic motivation towards mathematics (AMTM), thus showcasing the influence of culture on mathematical motivation. Confirmatory factor analyses and multi-group analyses were performed to investigate the reliability and validity of the Academic Motivation Towards Mathematics Scale (AMTMS) amongst Chinese Dai and Han students. According to the results, the AMTMS demonstrated a well-fitted seven-factor structure with satisfactory psychometric qualities, and measurement consistency was established. Furthermore, Han participants showed higher extrinsic and internal motivation levels, and lower amotivation level than their Dai counterparts. The extrinsic motivation-introduced regulation did not differ significantly between the Dai and Han groups. Further discussion is provided to explain these results, the study’s constraints, and their practical applications.