Research conclusions: The cut － and － cover tunnel will be constructed over the electrified railway for Chongqing －Huaihua in operation． According to the technology of“One cut － and － cover tunnel and one interval”，it solves the difficult problem of constructing subgrade of the cut － and － cover tunnel without impact on the regular operation of railway． The approach to the development of installing the“arch”steel tube brace for the transitional contact the way of suspension solves the difficulty of possibility of the electricity current cutting by which the catenary and locomotive in question are supported in case the existing pillars be removed． It originally makes the lining trolley in the arch ring which has the functions of lifting，sliding and anti － electric． It solves the problem that the lining trolley would not touch the contact wire while performing on the contact wire net and also protects the workers from the danger of electric shock．It could carry out the construction and guarantee the safety of operation at the same time with the arch ring of reverse templates． The above － mentioned new technology in construction is worthy being applied in the similar projects．