A multi-functional car seat gap filling device, comprising: an elastic rod-shaped body, at least one of the head and middle parts thereof being fitted with a storage pocket, and the tail part thereof being fitted with a through hole or an elastic band to engage a seatbelt buckle; an elastic band, one end thereof being attached to the bottom of the head of the rod-shaped body; and a small elastic ball or round stopper, which is fitted on the other end of the elastic band. The rod-shaped body is inserted into the top of a gap between the driver seat and storage compartment in a vehicle interior, the buckle of the driver seat safety belt passes through the through hole, and the small elastic ball or round stopper is locked into the bottom of the gap. The device functions to fill in gaps and hold small articles such as mobile phones, media players, and pens, rendering the vehicle interior neat and tidy and more conducive to safe driving.