Abstract: On the base of analyzing advantages and disadvantages of common tension device of belt conveyor,the paper designed ZYL type of hydraulic automatic tension device and introduced its structure composition,working principle and characteristics in details.The automatic tension device adopts hydraulic technology and converts oil pressure to axial movement of piston rod,thus tension trolley is drived to longitudinal move to change tension travel.The change of tension travel is converted to movement of tension cylinder of the belt conveyor so that to change tension of the belt and insures essential friction between belt conveyor and tension cylinder.It sets electric control cabinet to control running of hydraulic tension device and realizes local control and remote control.Actual application showed the hydraulic automatic tension device has steady running,reliable performance and convenient maintenance and adjustment,which can meet requirements of all kinds of running conditions of belt conveyor.