The invention relates to a yawing variable-pitch gearbox input end flange capable of monitoring oil leakage of oil seal. The yawing variable-pitch gearbox input end flange comprises an input shaft, a supporting bearing, the oil seal and a flange body, wherein the flange body is provided with big and small flange surfaces; a partition is arranged between the big and small flange surfaces; the big flange surface is connected to a box body of a yawing variable-pitch gearbox by virtue of a bolt and a locating pin to form a sealed cavity; the small flange surface is connected with an input end motor by virtue of a bolt to form a sealed cavity; the center of the partition between the big and the small flange surfaces is provided with an inner ring cofferdam; the input shaft passes through the partition, and is supported on the inner ring cofferdam by virtue of the bearing and the oil seal; an oil leveler and oil injection opening with a plug screw are arranged on the flange body wall of the box body side sealed cavity; an oil leakage observation hole is formed in the flange body wall of the motor side sealed cavity; the oil leakage observation hole is provided with a plug; lubricating oil in the box body side sealed cavity adopts bearing splash lubrication; and the oil seal prevents the lubricating oil from entering the motor side sealed cavity.