The invention discloses a mounting structure of a rear-row seat cushion, a fixing buckle and a vehicle. The fixing buckle comprises a buckle body and a lock core, a first opening for allowing a to-be-locked piece to penetrate into is formed in the buckle body, and the lock core is provided with a sliding part, an elastic deforming part connected with the sliding part and an unlocking part connected with the elastic deforming part. The sliding part is slidably contained on the buckle body, and the elastic deforming part is connected to the buckle body. In the process that the to-be-locked piece extends into the buckle body, force can be exerted to the sliding part, so that the sliding part is made to move towards the first direction so as to avoid the to-be-locked piece, and the elastic deforming part is stressed and deforms. After the to-be-locked piece crosses the sliding part, the elastic deforming part elastically drives the sliding part to be reset in the direction opposite to the first direction to lock a to-be-unlocked piece, and by controlling the unlocking part, the elastic deforming part can be driven to elastically deform so as to enable the sliding part to move towards the first direction to unlock the to-be-unlocked piece. Operation is easy, and locking is firm.