Fatigue life is very significant to the structural reliability of the equipment of nuclear reactor under primary water environment and has attracted much attention of many scholars and engineers. Because the fatigue cracks are more likely to initiate at surface discontinuities, the fatigue life is sensitive to the surface roughness of the materials. In this paper, an experiment was conducted to investigate the effect of the surface roughness on the fatigue life in a coolant environment and a numerical model was developed to predict the environmental fatigue life for 316LN austenitic stainless steel. Two types of surface roughness Ra=1.2 μm and 6.5 μm were conducted by low cycle fatigue tests with different strain rates, while the primary water environment and the loading strain amplitude were fixed. The experimental results show that the behaviour of the cyclic deformation exhibits the strain hardening in the initial stage, then the strain softening, and finally the instability and fracture. The fatigue life of the specimens with roughness shows a significant decrease comparing with that with smooth surfaces. Next, to establish the prediction model of fatigue life, an environmental fatigue correction factor Fen is defined as the ratio of fatigue life in air to that in a coolant environment. A surface roughness factor Aen is introduced to utilizing the curve of fatigue life in nuclear code ASME. In the proposed model, the effect of roughness on fatigue life is isolated by deducting it from the fatigue life in air, then it is considered in the corrected fatigue life calculation by coupling the influence of roughness and environment. Finally, the results revealed that the present prediction model coupling roughness and water environment can significantly reduce the influence of considering these two factors on fatigue life separately, which will provide guidance to improve the reliability of nuclear equipment.