Intra-die fluctuations in the nanoscale CMOS technology emerge inherently to geometrical variations such as line edge roughness (LER) and oxide thickness fluctuations (OTF). A full 3-D statistical simulation is presented to investigate the impact of geometrical variations on the FinFETs performance. In this work, roughness is introduced by a Fourier analysis of the power spectrum of Gaussian autocorrelation function. The influence of different geometrical variation sources is compared and summarized. The results shows that FinFETs performance is most sensitive to the fin LER, which causes a remarkable shift and fluctuations in threshold voltage, drain induced barrier lower effect (DIBL) and leakage current. The impact of gate LER follows that of fin LER. The simulation also suggests quantum confinement effect accounts for the aggressive fluctuations due to fin LER.