Cone Penetration Testing (CPT) serves as a useful in-situ tool for site investigation and soil characterization, while the end-bearing and shaft capacities of driven piles could be directly related to the CPT measurements. In terms of interpretation of CPT data, state parameter concept has been employed largely owing to its good indication of soil behaviour at different stress levels and densities. Drained cavity expansion solution in a unified state parameter model for clay and sand (CASM) is adopted in this paper for the applications to CPT in sands regarding to in-situ soil state. The effects of initial stress condition, friction angle and soil compressibility on the correlations between cone tip resistance, sleeve friction and state parameter are presented and discussed. The proposed method indicates the influence of initial state parameter on the evaluation of normalised penetration resistance, and the state parameter is directly related to the soil behaviour type index. The analysis contributes to the theoretical background of the framework for interpretation of CPT data.