The utility model relates to a full-aperture blowout preventer in a drilling tool. A valve body is internally provided with a channel; both a left valve plate and a right valve plate are of a semi- conical shape; outward-extending outer flanges are respectively arranged at the upper ends of the left valve plate and the right valve plate; the valve body is internally provided with an inner lug boss; and the outer flanges of the left valve plate and the right valve plate are hung on the upper end surface of the inner lug boss and is open to cause the channel to be in an unblocked state. The utility model has reasonable and compact structure and convenient use; conical valve plates can be completely opened and unblocked with the channel in the drilling tool in a normal circulation or static state, so circulating pressure consumption can be reduced, a valve core is basically not flushed; in addition, corresponding operations can be carried out by various instruments and tools the outside diameters of which are less than a certain size; when drill operation is carried out, once blowout happens in the drilling tool, the full-aperture blowout preventer of the drilling tool can automatically close under the push of liquid power so as to play a role of preventing blowout, and therefore greatly improve the treatment rate when underground accidents happen and improve the flushing resistance of the valve; and in addition, the full-aperture blowout preventer can further measure the pressure of a riser.