The signal quality and accuracy of the spatial filtering method for solid particle velocity measurement based on a linear electrostatic sensor array (LESA) are dependent on the spatial filtering characteristics of the LESA and particle distribution in a pneumatic conveying pipeline. In this paper, the charge induced on a circular LESA with different geometric sizes from a single particle having a unity charge is mathematically modeled. Furthermore, a dimensionless computation model of the sensitivity of the LESA is suggested based on a fitted cosine function to the finite-element calculation results of the mathematical model, and the spatial filtering characteristics and spatial selectivity of the LESA are quantitatively investigated based on the computation model. Experimental work was performed on a purpose-built particle flow test rig to verify the dimensionless computation model and the modeling results. Results obtained reveal that the LESA acts as a narrow-bandpass filter in the temporal and spatial frequency domains, and its spatial selectivity is closely related to the number, spacing, and width of the electrode. These results provide an important basis for the performance improvement and optimized design of the LESA for particle velocity measurement.