This paper presents verification and model based checking of the Trivial File Transfer Protocol (TFTP). Model checking is a technique for software verification that can detect concurrency defects within appropriate constraints by performing an exhaustive state space search on a software design or implementation and alert the implementing organization to potential design deficiencies that are otherwise difficult to be discovered. The TFTP is implemented on top of the Internet User Datagram Protocol (UDP) or any other datagram protocol. We aim to create a design model of TFTP protocol, with adding window size, using Promela to simulate it and validate some specified properties using spin. The verification has been done by using the model based checking tool SPIN which accepts design specification written in the verification language PROMELA. The results show that TFTP is free of live locks.