The invention belongs to the technical field of machines, and discloses a threadless connecting structure. When second bonding faces, third bonding faces and first O-type sealing rings on the two sides of an inserting male piece are bonded with a left inserting female piece and a right inserting female piece, self absorption is generated, and the inserting male piece, the left inserting female piece and the right inserting female piece are cured into a whole through bonding agents. After the left inserting female piece, the inserting male piece and the right inserting female piece are bonded and cured into a whole through the self absorption function, second O-type sealing rings are arranged in the outer surface of the whole, the whole is smeared with bonding agents and then inserted into a barrel, and the whole and the barrel are cured into a whole through the self absorption function. The size of a hole in the right side of the left inserting female piece is slightly larger than that of the outer circle on the left side of the inserting male piece, and the left inserting female piece and the inserting male piece are in clearance fit. The size of a hole in the left side of the right inserting female piece is slightly larger than that of the outer circle on the right side of the inserting male piece, and the right inserting female piece and the inserting male piece are in clearance fit. Through the threadless structural design, geometric space is effectively utilized, space waste is reduced, so that the structure is more compact, the structure is prevented from being invalid or redundant, and the threadless connecting structure is especially suitable for small space structures.