A length adjustable door lock includes a latch assembly, a lock core connected with the latch assembly, a lock bolt connected with the lock core, and a housing sleeved on the lock bolt. The latch assembly and the lock core respectively have an embedding opening and slot having matchable shape, wherein a buckling portion is formed and provided on the lock bolt coordinately, wherein the buckling portion is adapted for being assembled in the slot of the lock core through the embedding opening, which is easy for the assembling.