To guarantee safety operation and accumulate experience of large ship lock,we carry out the prototype observation of the miter gates in the third-line ship lock of Changzhou hydro-junction.The results show that the hoisting device is reasonable during the commissioning stage when the water level is equal in and out of the lock,for the miter gate system runs steadily,and the gate closing and opening forces are much less than the rated capacity of the headstock gear.At the beginning of the operation commissioning stage,there exists a serious over filling(over emptying)phenomenon in the ship lock.The great force in piston rod of the miter gates easily exceeds the capacity value of headstock gear with the damaged hydraulic lever.After the centralized control automation is implemented,the over filling(over emptying)phenomenon is controlled to a great extent,and the force in piston rod of the miter gates is within the normal capacity.The prototype test is an effective approach to ensure the safe operation of the practical engineering.