The utility model relates to a continuous cycle pup joint for well drilling. The continuous cycle pup joint comprises an outer casing, wherein an upper valve plate mechanism is arranged on the upper part in the outer casing, and comprises a clamping spring, a valve seat and straight-through valve plates which are connected with the valve seat by a hinged piece. The continuous cycle pup joint is characterized in that a bypass opening is formed on one side of the lower part in the outer casing; a lower valve plate mechanism is arranged at the bypass opening and comprises a bypass valve seat which is connected with the outer casing, a seal ring and bypass valve plates which are connected with the bypass valve seat by the hinged piece and a torsional spring; and a plug is arranged on one side of each of the bypass valve plates. The continuous cycle pup joint has the advantages that conversion between a bypass channel on a tool and a main channel which is connected with top drive is realized by utilizing double valve plate mechanisms on the continuous cycle pup joint for the well drilling, pump stopping circulation is avoided in the low-density balance well drilling process, the equal yield density of the circulation is maintained, and accidents such as the collapse of well walls, overflow, sand setting, the jamming of drill tools which are caused by pump stoppage are prevented. The continuous cycle pup joint is simple in structure, convenient to operate and low in manufacturing cost, the risks of well drilling operation can be reduced effectively, and the safety of the operation is ensured.