A self-assessment technique based on Fourier transform is presented to evaluate test environment of fiber optic gyroscope (FOG). Test results show that the zero bias stability of FOG is decreased to 0.0019 (°)/h (100 s, 1σ, that means the standard deviation after 100 s smoothing) in environment 4 from 0.0015 (°)/h (100 s, 1σ) in environment 3, and random walk coefficient is decreased to 2.8876×10 -4 (°)/h 1/2 in environment 4 from 2.1565×10 -4 (°)/h 1/2 in environment 3. Another FOG with pulse output is tested under different environments, whose zero bias stability is decreased to 0.0021 (°)/h (100 s, 1σ) in environment 4 from 0.0013 (°)/h (100 s, 1σ) in environment 3. The experiments of two FOGs demonstrate that the proposed self-assessment technique is effective, which provides guidance for the precision test of high precision FOG.