Novel thin film composite forward osmosis (TFC-FO) membranes were developed by using hydrophilic cellulose triacetate (CTA) porous substrates prepared by thermally induced phase separation (TIPS) method. A series of CTA substrates with different structures were fabricated to demonstrate the structure-performance relationship of the TFC-FO membranes. It is found that the substrates possess relatively large pores on their rough surfaces as well as their intrinsic hydrophilicity, leading to intensively large "ridge-and-valley" structures on the TFC-FO membranes. The large surface pores of the CTA substrates result in thick and rough polyamide skin layers. Moreover, the optimal CTA porous substrates should have a small thickness, high porosity, and oriented plate-like pores. These structures profit the TFC-FO membranes with superior water permeability, relatively high salt rejection, and low structural parameter. The one with thickness of 102 +/- 16 mu m and porosity of 87.1 +/- 1.1% shows the smallest structural parameter (516 mu m) and the desirable over-all properties in terms of water permeability and selectivity. It means that the hydrophilic CTA porous substrates enable to alleviate the internal concentration polarization (ICP) effect. These TFC membranes could provide a new route to develop high-performance composite membranes for FO desalination.