A computation algorithm for simultaneous chemical and phase equilibrium is proposed based on minimization of Gibbs free energy. By using the extent of reaction and the yield factor of phase

the computation of simultaneous chemical and phase equilibrium is transformed as into unconstrained nonlinear minimization problem

and is solved by Genetic Algorithm. The proposed algorithm has a wide application prospect because in this algorithm the variables are less

and negative mole-fraction

which usually appears in conventional algorithms

will not occur

and it can obtain a global optimization solution. The formaldehyde-water system is taken as an example.It is found that the computation results are just the same as those reported in the literature

which shows that the presented algorithm is robust and efficient.