In the context of the “double-decrease” policy, the construction of an after-school service system for primary and secondary schools is of great significance to the creation of a good educational ecology and the return of the public nature of education, and has become an indispensable part of the development of after- school services. Given the differences in resources, there are many problems with after-school services in Guizhou Province. Through the implementation of the survey on the white list of the number of afterschool services in Guizhou Province, and comparing the data between cities, it is found that the situation in the field of after-school services for primary and secondary schools in Guizhou Province has improved after the remediation, but there are still the following quality problems: unclear rights and responsibilities of the main body of after-school services, insufficient precision of the content of after-school services, lack of after- school services funding synergy, and an imperfect evaluation system of the results of after-school services. In order to solve these problems, this study proposes the following after-school service quality measures under the guidance of the concept of high-quality development of education: constructing a mechanism for the mutual sharing of rights and responsibilities among after-school service subjects, improving the accuracy of after-school service content, adjusting the mode of after-school service funding, and improving the evaluation system of after-school service quality. These measures are designed to improve the quality and effectiveness of after-school services in Guizhou's primary and secondary schools, to achieve high-quality development of after-school services in Guizhou's primary and secondary schools with the goal of the comprehensive development of students, and to promote the progress of education in Guizhou Province. Under the background of “Double Reduction” policy, the construction of after-school service guarantee system for primary and secondary schools plays an important role in the creation of good education ecology and the return of education publicity, and it is an indispensable part of the development of after-school service. Through literature research and field research, it is found that primary and secondary school afterschool services in Guizhou Province are facing quality assurance problems such as unclear rights and responsibilities of the main body of after-school services, insufficient precision of the content of after-school services, lack of synergistic funding for after-school services, and an imperfect evaluation system for the results of after-school services. Guided by the concept of high-quality development of education, a series of after- school service quality assurance measures are proposed to build mutual sharing of rights and responsi- bilities of after-school service subjects, enhance the accuracy of after-school service guarantee contents, adjust the mode of allocation of after-school service guarantee funds, and improve the evaluation system of after- school service quality assurance, aiming to improve the quality and effectiveness of after-school services in Guizhou's primary and secondary schools, and realize high-quality development of the quality assurance of Guizhou's primary and secondary schools' after-school services, with the aim of promote the overall development of students as an important goal, so as to achieve the ultimate goal of promoting the progress of education in Guizhou Province.