A detachable and combined drive key of a power head of a rotary drilling rig is provided. The drive key includes torque transfer keys and a pressure transfer key. Each torque transfer key is respectively assembled on a key groove on an inner wall of the drive sleeve. The pressure transfer key is assembled at a bottom of a drive sleeve and includes a circular ring structure and a plurality of pressure pads. Each pressure pad has a width less than the torque transfer key. A central surface of each pressure pad is aligned with a central surface of each torque transfer key. The drive sleeve, the torque transfer keys, and the pressure transfer key are combined to form an integrated drive key with a same circular cross-section.