The seventh national census data show that China’s total fertility rate has dropped to 1.3, which is at an extremely low level. Over the past five years, the number of children in the early childhood age group has continued to decline, which has had a significant impact on the development of preschool education. Preschool education has shifted from the stage of scale expansion to the stage of quality improvement. Based on this, this study focuses on optimizing the training model for early childhood teachers under the background of low fertility rates, clarifying the necessity and urgency of teacher training in this context; analyzes the impact of population structure changes on preschool education and analyzes the existing problems in the current training model for early childhood teachers; points out the problems from three aspects: scale, curriculum, and assessment mechanism, and propose specific optimization countermeasures; strengthens scale regulation, rebuilds the curriculum system, and constructs a diversified assessment mechanism. These research results are helpful in establishing a teacher training system that adapts to the population development trend, improving the quality of preschool education. Promote the transformation of teachers towards a high-quality direction and promote the long-term healthy development of preschool education.