The ultra-stable laser is a key component in optical lattice clock, whose frequency stability is limited by the thermal noise and affected by the temperature fluctuation of ultra-stable cavity. Thus the temperature fluctuation is a serious obstacle in pursuing thermal-noise-limit of ultra-stable laser. In this paper, we analyze the requirement of the temperature stability to reach the thermal-noise-limit in frequency domain and time domain, and design the thermal-isolation vacuum system (with one passive thermal shield layer and two active temperature stabilized layers) and the corresponding temperature controller. Having developed the ultra-stable cavity system, we measure the zero-expansion work temperature of the ultra-stable cavity, the temperature transferring time constant of the thermal shield (3.6 d), and the temperature fluctuation of the temperature stabilized layer in vacuum in 11 d (<1 mK). With these data, we calculate the temperature fluctuation of the ultra-stable cavity, and evaluate that the frequency noise induced from the temperature fluctuation which is all below the thermal-noise-limit in 1000 s integration time. Moreover, we also use the clock transition spectrum of the 199Hg cold atoms in magneto-optical trap to measure the long-term drift rate of the ultra-stable cavity (4.2 kHz/d). This frequency drift rate of ultra-stable cavity is competent to mercury optical lattice clock.