The invention provides a novel assembling method for a eccentric valve. The assembling method comprises the following steps that a valve seat is assembled in a valve body; an inner shaft sleeve is arranged in a front shaft hole; a sealing element is arranged on a valve element, and then an adjusting cover presses against the sealing element; the valve element is arranged into the valve body in a hoisted mode; an outer shaft sleeve and a front shaft are inserted into the front shaft hole; a rear shaft penetrates through the valve element and a rear shaft hole, and a bearing cap is arranged in the rear shaft hole and sleeves the rear shaft; fourth screws on the bearing cap are adjusted; first screws on the adjusting cap are adjusted; and finally, sealing rubber gaskets and a valve deck sequentially sleeve the valve body. The assembly method has the advantages of being convenient, rapid and capable of realizing on-line maintenance and replacement of parts inside the valve body, the wholevalve does not need to be disassembled from a system, and the working efficiency can be improved.