In this talk, I will introduce the Perron method for the classical Dirichlet problem. First, the critical point of the Perron method, we construct a harmonic function in the domain by using subharmonic functions. Secondly, we will investigate some proper conditions for domain; When the harmonic function from the Perron method coincides with the given function on the boundary of domain? In this step, we use the concept of barrier function with respect to the domain.