Bridge crane function analysis of portal crane is a kind of used for lifting, lay down and carry heavy items, and making the weight within a certain range of lifting, handling equipment, play an important role in the process of production. Portal crane system is divided into hoisting, luffing, rotating, walk four parts. Portal crane load characteristics of the portal crane organizations are in constant torque load; In addition, the different institutions also have their own characteristic. Lifting mechanism due to the heavy things in space has potential energy, is a potential energy load. Its characteristic is: weight rises, motor to overcome all kinds of resistance (including the weight of gravity, friction resistance, etc.) and work, belongs to the resistance load; Weight falls, due to the weight itself has the ability of decrease in acceleration of gravity (potential), so when the weight of gravity is greater than the transmission mechanism of the frictional resistance, the gravity of the weight itself (who) is the power of falling, motor became the recipient of the energy, belongs to the dynamic load; But when the gravity of the weight is less than the transmission mechanism of the friction resistance, heavy things still need to drag down by motor, belonging to the load resistance. Amplitude, rotating, walk institutions are load resistance. But outdoor crane these institutions sometimes become dynamic load under a strong wind. Bridge crane speed control method of each part of the portal crane drag system generally.