The invention discloses a device and method for detecting the hardness of a spherical cover part. The device comprises a hardness testing machine and a long pressure rod, the test table of the hardness testing machine is fixedly provided with a tool main body, the long pressure rod is arranged between the hardness testing machine and a pressure head and is used for prolonging a distance between the testing machine pressure head and the hardness testing machine, the tool main body is provided with an oblique plane, the oblique plane is fixedly provided with a positioning boss, the positioning boss is in clearance fit with a hole in the bottom of the spherical cover part to be detected, and when the spherical cover part to be detected is fixed on the oblique plane, the relative plane part ofthe spherical cover part to be detected is positioned in the horizontal position. The device for detecting the hardness of the spherical cover part solves a problem that the surface Rockwell hardnessof the internal surface of the spherical cover is difficult to detect, and ensures the accuracy and the reliability of a detection result.