Transport of thermal-driven ions in porous materials has not been clearly explained yet, while this transport has great application potential in co-generation of vapor and electricity for a bi-layer seawater desalination system. In this work, by taking into account the actually structure of a porous material, we theoretically modeled the thermal-driven ion transport in a porous material and also the resultant current and potential produced by such a transport. With models solved by the finite element method, it turns out that a porous material with a cross section of 30 x 10 mm(2) could give a thermal current of about 27.2 mA, a thermal potential of about 63.7 mV, and a thermal power of about 433.2 mu W, which are large enough to drive commercial electronic devices. This work provides a possibility of a vapor electricity co-generation in a bi-layer desalination system.