A toilet seat cushion with an adjustable installation length comprises a toilet seat cushion body and an installation length adjustment structure; the installation length adjustment structure is disposed at the rear end of the toilet seat cushion body; the installation length adjustment structure comprises a connecting member and a fixing member; the connecting member is movably connected to the rear end of the toilet seat cushion body; the fixing member comprises two side plates and a positioning plate; the two side plates perpendicularly extend forwards from two ends of the positioning plate respectively; each side plate is provided with an installation hole used for installing the toilet seat cushion body; the positioning plate is detachably positioned onto the connecting member; in this way, the center of each installation hole has a first position and a second position, and the center of each installation hole switches between the first position and the second position with the cooperation of the positioning plate and the connecting member; by means of the structure, the installation length of the toilet seat cushion is adjustable, and accordingly, the toilet seat cushion can match toilet bases with different specifications, thereby improving the applicability of the toilet seat cushion.