An 1-D pulse FEL simulation code is applied to study the accelerator noise effects on CIAE far-infrared FEL oscillator. The laser power instability and spectral center shift due to the time jitter and energy ripple of the electron micropulse are modeled by the code, and the roles of the noise frequency, amplitude as well as the optical cavity detuning in the noise effects on the FEL are exhibited in the simulation.