The present invention relates to a ladder for loading/unloading agricultural machinery and an assembling method of a structure of the ladder, and more particularly to a ladder including a first ladder structure, which includes: a plurality of vertical frames including horizontal inserting grooves at front and rear ends of each vertical frame, corresponding to each other, to allow horizontal bars to be inserted into the grooves in the same direction, horizontal reinforcing bar inserting grooves formed at a side surface thereof, a link connection part formed at one end thereof to be coupled to a loading box of a vehicle, and a connection bracket formed on the other end to be coupled with a second ladder structure, wherein the vertical frames are installed, at each predetermined interval from right and left sides, on upper surfaces of the vertical bars fixed in an assembling zig a first hydraulic system fixing bracket installed at space between the vertical frames in the center to be connected to a hydraulic system installed at the vehicle in order to rotate the ladder structure at a rear end of the loading box depending to the expansion operation of a hydraulic system a plurality of horizontal reinforcing bars installed at space between the plurality of vertical frames, respectively, in such a manner that both ends of each bar are inserted into horizontal reinforcing bar inserting grooves formed in each side surface of the plurality of vertical frames and footplates provided to supply each passage to both sides of the upper surface of the vertical frame of the ladder structure, which is formed after welding jointed part between the horizontal bars and the vertical frames and each jointed part between the vertical frames and the horizontal reinforcing bars and a second ladder structure, which is assembled by horizontal bars, vertical frames, horizontal reinforcing bars, and footplates in the same method of assembling the first ladder structure and has a structure same
