The invention relates to a manufacturing method of a drainage bottle. Firstly, a bottle body with an opening and a bottle cap corresponding to the opening shape are respectively produced through the plastic shaping process, and a continuous and closed weld line according with the shape of the upper edge of the bottle body is arranged on the bottle cap; secondly, the bottle cap is fixed and connected at the upper edge of the bottle body by adopting the ultrasonic welding process, and then the bottle cap is covered above the opening in a sealing way. The adopted injection molding process for manufacturing the bottle body, and the bottle cap is simple, the product quality is greatly improved relative to the blow molding process, and the sand holes or micro-air holes generated in the blow molding process are eliminated. The absolute air tightness at the juncture of the bottle body and the bottle cap can be ensured by adopting the ultrasonic welding, and the air leakage hidden danger possibly existing in the mechanical sealing method can be thoroughly stopped.