Numerical analysis of MHD flow in rectangular channel is performed to evaluate the performance of remountable first wall with liquid blanket like Li or Flibe, where fabrication and maintenance of the system become extremely simplified. Four-channel model is used to calculate the MHD pressure drop in variously coated channels. The effect of crack existence in the coated layer of flow channel on the MHD pressure drop is also evaluated for real usage. The numerical results indicate that some amount of crack existence is allowable, which shows possibility to apply the first wall concept to future fusion reactor design.