We report on the development and performance evaluation of an ultra-stable laser for an ²⁷Al⁺ optical clock. After a series of noise suppressions, especially the vibrational and temperature fluctuation noise, the 30 cm long cavity stabilized laser obtains a frequency instability of 1.3×10⁻¹⁶@1 s. This result is predicted by noise summation and confirmed by the three-cornered hat method. The ²⁷Al⁺ optical clock transition is also used to characterize the laser frequency noise, and consistent results are yielded. This is the first reported instance of using single ion optical clocks to measure the frequency noise of ultra-stable lasers, as far as we know. With the implementation of the ultra-stable clock laser, an ultra-narrow linewidth clock transition of 2.8 Hz is obtained.