The utility model relates to the technical field of oil-gas field operation tools, in particular to a built-in annulus bottom hole pressure measuring device which comprises an outer cylinder, a mandrel, a pressure transmission plug and a measuring instrument assembly. The measuring instrument assembly comprises a power supply, a pressure sensor and a data storage, an instrument bin is axially arranged inside the mandrel, an annular projection is arranged on the outer side of the upper portion of the mandrel, an overflowing hole is axially formed in the annular projection, at least one first hole is radially formed in the annular projection, the measuring instrument assembly is mounted inside the instrument bin, a mandrel abutting cylinder is connected with the lower end of the mandrel, the pressure transmission plug is fixedly mounted on the side wall of the outer cylinder, and a central hole of the pressure transmission plug is communicated with the first hole. A mandrel sealing structure is closely matched with the outer cylinder, drilling fluids in a drilling tool are effectively isolated, the annulus drilling fluids can be guided into the instrument bin inside the mandrel, so that pressure and temperature are measured, and the built-in annulus bottom hole pressure measuring device has the advantages of safety, capability of saving labor, simplicity, convenience and high efficiency.