Abstract: Tensile fatigue S-N curves and conditions fatigue strength of aviation perspex were obtained by tensile fatigue test and effect of stress ratio on fatigue properties of the aviation perspex was studied. The results show that the conditions fatigue strength of the perspex were 63.0, 57.3, 48.4 MPa under the condition of stress ratios were 0.4, 0.1, －0.4. The tensile fatigue S-N curves integrally moved up with the increase of stress ratio. Under the same stress level, specimens tested with higher stress ratio had longer fatigue life.