In this paper, a statistically sound "atomistic" approach for analyzing random impurity effect in nanoscale device is presented. The quantum confinement aspects associated with the coulomb potential wells of individual impurities are treated using the density gradient approach applied to the channel carriers in a hydrodynamic framework. The statistically generated large-scale doping profiles are similar to the physical process of ion implantation and the number of impurities inside channel follows normal distribution. Discrete dopants are statistically positioned into the three-dimensional channel region to examine associated carrier transportation characteristics, concurrently capturing "dopant concentration variation" and "dopant position fluctuation". Our preliminary study extensively examines the threshold voltage fluctuations of various device structures, single-, multiple-, nanowire surrounding- and nanowire omega-gate. The presented approach is cost-effective in fluctuation analysis.