In this work, a novel sulphonated poly(ether ketone) (SPEK) polymer with super-hydrophilic nature was designed as the substrate material to fabricate high performance thin-film composite (TFC) membranes for desalination via forward osmosis (FO). m-Phenylenediamine (MPD) and 1,3,5-trimesoylchloride (TMC) were employed as the monomers for the interfacial polymerization reaction to form a thin aromatic polyamide selective layer. It has been demonstrated that blending a certain SPEK material into the polysulfone (PSU) substrate of TFC-FO membranes not only plays the key role to form a fully sponge-like structure, but also enhances membrane hydrophilicity and reduces structure parameter. The TFC-FO membrane comprising 50 wt% SPEK in the substrate shows the highest water flux of 50 LMH against deionized water and 22 LMH against the 3.5 wt% NaCl model solution, respectively, when using 2 M NaCl as the draw solution tested under the pressure retarded osmosis (PRO) mode (draw solution flows against the selective layer). It is found that the hydrophilicity and thickness of the substrates for TFC-FO membranes play much stronger roles in facilitating high water flux in FO for desalination compared to those made from hydrophobic substrates full of finger-like structures. Moreover, the reduced membrane structural parameter indicates that the internal concentration polarization (ICP) can be remarkably reduced via blending a hydrophilic material into the membrane substrates. Thermal treatment of TFC-FO membranes with optimized conditions can also improve the membrane performance and mechanical strength.