A patched cleaning model was proposed for the pressure drop in a bag filter. in which the filter cloth had two surface areas, i.e., the area with residual dust with the specific resistance zeta(D) and the area fraction epsilon(D), and the perfectly cleaned area with zeta(C) and epsilon(C). The measured pressure drop under the batch filtering operation coincided well with the calculated one with the patched cleaning model through the operation time. Also. the measured pressure drop in a three-compartment bag filter under the continuous filtering operation coincided well with the calculated one with the proposed model by using the specific resistance of dust cake alpha, the specific resistances of filter cloth zeta(D), zeta(C) and the area fraction epsilon(C) that were determined experimentally for the batch filtering operation, though the specific resistance of filter cloth with residual dust epsilon(C) needed to be corrected for the continuous filtering operation. The velocity dependency of the specific resistance of dust cake alpha did not affect the calculation of the pressure drop under the batch filtering operation, though the velocity-dependent alpha gave a slightly smaller calculated value of the specific resistance of filter cloth with residual dust zeta(D) in the three-compartment bag filter under the continuous filtering operation than the constant alpha. However, the evolution of the pressure drop under the continuous filtering operation was almost independent of the velocity-dependency of alpha.