The invention discloses an underground-excavation shallow-covering large-cross-section tunnel construction method. The method includes the following steps of a, closing and water reducing; b, cross section dividing; c, excavation of caves on the two sides, supporting and reinforcing; d, excavation of a middle cave, supporting and reinforcing; e, primary support back grouting and forming of a bottom secondary lining; and f, closing of an arch secondary lining into rings and back grouting of the secondary lining. By means of the underground-excavation shallow-covering large-cross-section tunnel construction method, a large cross section is divided into small cross sections, closed-ring construction is adopted, supporting of each small cross section is reinforced, and finally the whole cross section is supported in a closed-ring mode; the working condition that soil bodies of an excavated tunnel face are loosened and run off due to water leakage and seepage of shallowly-covered concealed pipelines can be effectively dealt with, meanwhile, all procedures are tightly connected, construction and dismantling of temporary supports are easy compared with a CD method or a CRD method, sedimentation deformation of the whole cross section is well controlled, and the project progress is rapid. Compared with a shield method, the construction method can adapt to zones with variable cross section sizes, and meanwhile the project cost is greatly lowered.