The drag forces of particles aligned in a line parallel to the direction of relative motion between the fluid stream and the particles are investigated. The particle-particle interactions and the wake effect should be taken into account for quantitatively describing the drag force of the interactive particle. Under the circumstances of the Reynolds number (Re) being around 100, the drag force of the interactive trailing particle is analyzed based on the velocity distribution in the far wake region downstream of the leading particle. As a result, a semianalytical expression for the drag force of the trailing particle is formulated. It is utilized to calculate the drag force ratio of the trailing particle for Re of 54-154. Agreement between the calculation and the measured data is achieved.