The invention relates to a truck-frame side beam and crossbeam connecting joint totally-butted structure which is characterized in that the totally-butted connection of a side beam and a crossbeam is realized through a connecting seat, a plate-plate butt-joint structure is formed by a side beam connecting end and a side beam inner vertical plate, and a pipe-pipe butt-joint structure is formed by a crossbeam connecting end and the crossbeam. A assembly-welding process method comprises the assembly welding of the connecting seat and a crossbeam pipe, the assembly welding of crossbeam composition, the assembly welding of the connecting seat and the side beam inner vertical plate as well as a guide pole, the assembly welding of a side beam reinforcing baffle plate and an upper cover plate and the assembly welding of a whole frame. The invention realizes the totally-butted connection of the side beam and the crossbeam of the frame through a new connecting joint of the side beam and the crossbeam, breaks through a traditional process of forming the frame after both the side beam and the crossbeam become finished products, and has the advantage superior to the angle connecting structure or the angle-connecting and butting combined structure of a traditional structure and greatly superior to an overlapping structure. A welding joint has the minimum stress concentration, the minimum welding filling quantity and the minimum welding residual stress and deformation; the structural shape is continuous and attractive; and the bearing capacity and the anti-fatigue capacity are strong.