In recent years the fertility rate of population has been dropping rapidly in Taiwan. The Population structure presents declining birthrate. The amount of population influences the educational demand directly, and relates to influence the whole development of education and the scale of school. Declining birthrate has a great influence in the educational system. In the school's system, the elementary school doesn't worry about enrolling new students originally, but now also has the pressure of for existence. The source of students reduces rapidly, and a lot of schools have difficulties in management, and face many problems, such as ”shortage of students”, ”reduction of classes and teacher surplus”, and so on. The article analyses the cause of declining birthrate, and then investigates the influence of declining birthrate in the elementary school. To take the Forest elementary school (assumed name) as an example, the article discusses the impact of declining birthrate. Finally, the article gives some suggestions and strategies for elementary schools to slow down the impact of declining birthrate.