There exists a very interesting feature in SAT(satisfiability) problem. With a fixed numbers of variables, the satifactory probability of an SAT instance change sharply from 1 to 0 while the number of clauses increasing, and the phase transition point is estimated to be K≈4.3*N. The phase transitions are of great importance to the efficient algorithms designing to solve the SAT problem. More generally, the phase transition of 2-3-SAT problem was discussed in this paper. The analysis of the location of the phase transition point of 2-3-SAT shows that there is an linear ratio between a 2-clause and a 3-clause in the sense of the constraint power which could help to design a more powerful heuristic for algorithms designing.