The study explored the relationship of L2 motivational self system and motivated effort to L2 speaking proficiency through structural equation models. Results indicated that effort affects L2 speaking proficiency directly, and actual effort’s explanatory power is the biggest among all the independent variables. Motivational variables affect L2 speaking proficiency indirectly via effort, among which ideal L2 speaking self and attitudes to L2 speaking are the biggest contributors to L2 speaking proficiency, while ought-to L2 speaking self plays a limited contributing role. L2 speaking instrumentality-promotion, self-confidence, and speaking interest inter-correlate with each other, and serve as supporting variables to shape ideal L2 self, and affect L2 speaking proficiency indirectly. Instrumentality-prevention and family influence inter-correlate with each other, together with instrumentality-promotion, serve as supporting variables of ought-to L2 speaking self, and have limited and indirect influences on L2 speaking proficiency.