This research is an attempt to develop a numerical method for studying some of the basic relations that govern particle interaction in laminar flow field so as to (1) acquire better understanding of the flow phenomena and (2) extend the knowledge of the derived analytical results for the modification of the existing formulas. The study model consists of two parts. The first part is to investigate the effect of particle spacings (or concentration) and specific gravity on the particle drag coefficients when particles settle in groups in a given fluid. The study is to establish a relation between drag coefficient and concentration in Durand's Formula, which at present implies that the former is independent of the latter. The second part attempts to analyze, by solving the non-linear differential equation, the translation, rolling, lifting of circular particles flowing in long horizontal channel in the laminar regime, so as to correlate the geometric parameters with the hydraulic parameters.