The notion of rank of divisor on graph was introduced by Baker and Norine in 2007 in showing the link with the similar notion on Riemann surface. Moreover, the authors have developed a theorem for divisors on graph analogue to the classical Riemann-Roch theorem. Since then, many works have studied for computing the rank of divisors on graph. A very important is the new theorem on the NP-hardness complexity of the Problem of computing the rank of divisor on general graph. The proof of this result was based on the proof of the NP-hardness of the Problem of finding the minimum recurrent configurations of Chip Firing Game on directed graphs (by Perrot and Pham). In this talk, we will present some (linear) algorithms for computing the rank of divisors on some classes of graphs.