ABSTRACT: Pretension plays a critical role in providing active support to control roof sagging and bedding plane slippage in underground coal mines. However, the optimal amount of pretension for cable bolts to achieve effective ground control remains unknown. Applying excessive pretension on cable bolts may cause cable bolt failure. On the other hand, insufficient pretension is ineffective in preventing large roadway deformation and roof fall incidents. This paper investigates the pretension effect on cable bolts at various geological conditions for underground coal mines. A numerical model based on a coal mine in the Western Coalfield, NSW has been developed by considering the variance of in-situ stress, bedding plane and claystone properties. Model results focused on analysing the pretension effect on the cable bolt force distribution and bond failure along the cable bolts. The overall bond failure along the cable bolts at different geological conditions was also analysed with different pretensions. The neutral point, where relative shear movement between the cable bolt and rock mass is zero, is considered as a key position along the cable bolt to describe its loading behaviour. The results suggest that inappropriate high pretension would promote bond failure. This paper is expected to provide a theoretical guidance for applying optimal pretension in the coal mining industry.