First, a frequency doubling model with 4-dimensional temperature-beam coupling was proposed in this paper on the assumption of an infinite transverse crystal section. The frequency doubling process, by using analytical formula and iterative method, was simulated in the BBO crystal pumped by a laser with watt-level power. The amplitudes and conversion efficiencies of the fundamental, and harmonic beams and temperature distributions were obtained, together with the time evolution of temperature field and beam intensities. The influence of the pumping power and crystal length on the conversion efficiency and temperature field was analyzed secondly. The results finally showed that the temperature distribution has great influence on the conversion efficiency and beam quality. A compensation for the phase mismatch induced by temperature can well improve the reduction of conversion efficiency induced by the thermal effect, which thus should be considered in practice.