This series of tower cranes, ranging from QTZ31.5 to QTZ315 has a horizontal jib frame, a jib trolley radius chang mechanism and a hydraulic self-raising mechanism. It is original in design, reliable in operation and satisfactory in shape. Equipped with necessary safety devices, these cranes show good speed-control capacity, satisfactory operat stability and high work efficiency .It can be widely used for construction of high-rise hotels, residential buildings, high-rise industrial buildings, large-span factory buildings and tower-like buildings like tall chimneys.