This paper provides a new method to fabricate an integrated Janus fabric that has excellent unidirectional water‐penetration property. Based on commercial polyester fabric that is pretreated with CaCl2 solution, polyvinyl alcohol/sodium alginate (PVA/SA) solution is deposited directly on the fabric via electrospinning and in situ chelated with Ca2+ contained in the fabric. The in situ formed PVA/SA gel coating not only transfers the surface of polyester fabric from hydrophobic to hydrophilic but also retains original porous structure of polyester fabric. As the water droplet contacts with unelectrospun side of modified polyester fabric (M‐PET) pretreated with 10 wt% CaCl2, it penetrates through the M‐PET within 1 s from unelectrospun side to electrospun side after application, and disappears on unelectrospun side within 2 s, and in turn, droplet spreads out on electrospun side of M‐PET within 2 s after application and no penetration occurs. The M‐PET pretreated with CaCl2 solution has outstanding antistatic property, vapor, and air permeability. The impact of ratio (v/v) of the PVA and SA solution and the concentration of CaCl2 pretreating solution on properties of the M‐PET are investigated.