The crosssection size and quality of composite lining of railway tunnel constructed by mining method has many problems such as excavation forming, overbreak and underbreak, and difficult to control lining thickness. The problems of crosssection size including presetting, construction error, section measurement, underbreak treatment, thickness and square quantity of concrete of secondary lining, etc.〖KG-*3〗, are analyzed based on the design and construction practice of composite lining of highspeed railway doubletrack singletube tunnel. Based on the concept of the strict control of overbreak and underbreak of lining, countermeasures and suggestions are put forward from the aspects of tunnel crosssection size presetting and adjustment, section measurement method, underbreak treatment and primary support surface dressing, calculation of concrete volume of secondary lining pouring by arch wall lining trolley, section size quality control measures, etc.