Provided are a tool and a method for injecting cement into the top of a horizontal well screen pipe without drilling and plugging. The tool for injecting the cement into the top of the horizontal well screen pipe without drilling and plugging is composed of a drilling-free and plugging-free tool, a bumping pressing rubber plug and a fishing tool. During construction, the drilling-free tool is lowered to the well along with a sleeve bunch. A well mouth is pressurized, a packer is sealed through expansion, pressurization is continued, a starting piston is opened, circulation is built, and well cementation is conducted normally. The bumping pressing rubber plug is added for bumping pressing at the later stage of the well cementation, the piston is closed simultaneously, a circulation channel is closed, and the well cementation is finished. After cement curing is finished, fishing is conducted through a small drill pipe connected with a fishing anchor, the small drill pipe and the fishing anchor are lifted after being in place, slips are opened, a fishing drum is blocked, an internal structure of the drilling-free tool is lifted together, and construction is finished. During a working process, a well completion accessory used in the process is not affected by drilling and grinding, service life is greatly prolonged, diameter in a well completion pipe column is large, the inner surface of the well completion pipe column is smooth, and smooth implementation of acid washing and gravel packing is guaranteed. Well completion working time of a single well is reduced by 24 hours on average, and well completion cost is greatly saved.