The drying phenomena of an initially filled perfectly wetting liquid in a square internal cross-sectional tube are studied. The conditions are such that the liquid films develop along the tube internal corners under the effect of capillary forces until the bulk meniscus recedes in the tube. In this work, the Shan-Chen Lattice Boltzmann method (SC-LBM) is implemented to elucidate the complex multiphase phenomena involved in the isothermal drying of the square capillary tube. The SC-LBM is validated with Stefan-Maxwell diffusion relation and the simulated drying kinetics are in very good agreement with the commonly observed drying phenomena, which are the constant rate period (CRP) followed by the falling rate period (FRP). The computed capillarity along the liquid-gas interface at the internal corners of the tube results in the formation of extended corner films and surface films. Further, the pinning and the depinning phenomena as well as the variations of the corner film width are studied in detail. Based on the roughness factor of the tube, the characteristics of drying kinetics are studied and compared with the smooth square capillary tube.