Based on using the Acousto-optic Modulator （AOM） as a feedback device， we design the power locked setup of the 780 nm laser in the common band of atomic clocks. Through low-noise design and parameter optimization， the suppression of key sources of the noise and the laser power locking are achieved. In the frequency deviation range of 20~10 000 Hz， the relative intensity noise of laser beam is effectively suppressed. Especially at the frequency of 1 300 Hz， 20 dB suppression of RIN has been reached. At the same time， the relative power stability in the mid-term （9 000 s） has been increased 78 times from ±0.754% to ±0.009 68%. According to the typical parameters of CPT atomic clock， the influence of relative intensity noise of the laser on the frequency stability of an atomic clock is only 2.1×10^–14@1 s. In addition， the mid-term stability improved from 4.67×10^-2 in unlocked state to 8.67×10^-5 in locked state，and it will be helpful to improve the intermediate period frequency stability of the atomic clock.