The invention discloses a cotton filling machine with an adjustable cotton filling opening. The cotton filling machine comprises a cotton filling machine body and the cotton filling opening formed inthe cotton filling machine body, the cotton filling opening comprises a cotton filling opening assembly and a guiding assembly, wherein the cotton filling opening assembly comprises a first matching plate and a second matching plate which are correspondingly distributed in the circumferential direction, the second matching plates are located on the inner layers of the first matching plates, and the first matching plates and the second matching plates are the same in number and staggered; a driving rod and a pair of longitudinally-distributed first hinge seats are fixed to the outer side face of each first matching plate; and the guiding assembly comprises a guiding cylinder and a fixing ring located at the edge of the inner end of the guiding cylinder, the guiding cylinder sleeve the periphery of the cotton filling opening assembly, second hinge seats corresponding to all the first hinge seats are distributed at the upper edge of the guiding cylinder in the circumferential direction, and all the second hinge seats are connected with the corresponding first hinge seats through connecting rods. According to the cotton filling machine with the adjustable cotton filling opening, through rotation, the size of the cotton filling opening can be adjusted to adapt to different use scenes, and flexibility is good.