The utility model discloses an add oil pipe, including installing the body on the organism, install on the upper portion of body can be with the sealed lid of body open -top department, the flange is installed to the lower part of body, the body lower part is passed the flange and is formed the prolonged downward section that can stretch into in the organism, the prolonged downward section can realize the fixed of body, the assembly of body on the organism of being convenient for, the flange passes through the bolt -up on the organism, improve the reliability of body installation, the lateral part of body is installed the oil and gas separator who communicates with pipe body inner cavity and is returned pipe joints, vertical tangent plane that oil and gas separator returned pipe joints is " U " shape, consequently, can there be one section oil body in oil and gas separator in returning pipe joints all the time, just so can prevent in the crankcase oil gas to flow back among the oil and gas separator, this kind of structure has replaced oil and gas separator and has returned the oil pipe check valve, the labor intensity of the assembly personnel is reduced, the efficiency of the engine asseumbly is improved.