The invention provides a wellhead blowout prevention device of a rod-pumped well and a blowout prevention method used during wellhead opening operation. The wellhead blowout prevention device of the rod-pumped well comprises a blowout prevention short section. A blowout prevention screwed plug is detachably arranged at the top end of the blowout prevention short section. A first connector detachably connected with the upper end of a Christmas tree is arranged at the bottom end of the blowout prevention short section. An inner cavity of the blowout prevention short section is matched with a sucker rod inside the Christmas tree. A sucker rod hanger is arranged in the blowout prevention short section. A step is arranged on the inner wall of the blowout prevention short section and separated from the bottom end by a first distance. The sucker rod hanger is supported on the step. A plug which can be inserted into the sucker rod and connected with the sucker rod is formed at the bottom end of the sucker rod hanger. By means of the wellhead blowout prevention device of the rod-pumped well and the blowout prevention method used during wellhead opening operation provided by the invention, the effect that when a wellhead needs to be opened for operations of replacement of the sucker rod, plug removal with forward extrusion, well washing and the like, occurrence of a blowout accident is prevented, and the purpose of blowout prevention is achieved is guaranteed. The wellhead blowout prevention device of the rod-pumped well is simple, convenient to operate and safe in operation.