We study the phase transition in a steady temperature-nonuniform system in the frame of the Ising model. We calculate the nonuniform-temperature effects on the phase transition point, the fluctuations, and the correlation length of the order parameter. We find the phase transition could happen at a temperature higher than the equilibrium phase transition temperature of a temperature-uniform system. Besides, the fluctuations and the correlation length are enhanced near the phase transition point, and they monotonously increase from the crossover regime to the first-order phase transition regime without exotic behavior at the critical point. Our study is helpful to understand the behaviors of QCD phase transition in the relativistic heavy-ion collision and provides a method to evaluate the nonuniform-temperature effects for the order parameter.