To achieve a highly stable strontium atomic optical clock, the ultra-stable laser system based on 30 cm cavity is desiged. Systematic evaluation and suppression of the main noise in the system is performed, so that the current vibration insensitivity of the reference cavity is reduced to 6×10^-10/g with the corresponding frequency instability less than 3.6×10^-16. By using the method of temperature control in the vacuum chamber, the temperature changes is less than 0.4 mK in a day, and the temperature fluctuation of the cavity is 5 orders of magnitude lower than the laboratory environment temperature at 1 Hz. The power jitter is suppressed to 1 pW, and the corresponding frequency instability is 2.4×10^-19@1 s. The residual amplitude noise and fiber phase noise are less than 3×10^-16 after being suppressed, which fully meets the requirements for ultra-stable lasers of the order of 10^-16. Comparing the beat frequency with a 10 cm cavity ultra-stable laser system, comprehensive beat frequency results and noise analysis show that the stability of the laser frequency instability is less than 6.2×10^-16@1s after the system locked.