Cross-flow-induced vibration of slender cylindrical in thermal environment was researched. The partial differential equation of the system was reduced to an ordinary differential equation by the Galerkin's method. The influence of thermal load on the system critical flow velocity was analyzed, and the bifurcation region of the system and the distribution in the parameter space were obtained by the numerical method. The character of motion was discriminated by application of the bifurcation diagram and phase portraits. The analysis shows the system with changing parameters appears a periodic motion, and the critical fluid velocity of the flutter decreases with increasing temperature. When the temperature load is at constant with the increasing flow velocity, the amplitude of period motion of the system became more and more big. The system shows limit cycle oscillation, periodic-3 motion, quasi-periodic and chaotic motion.