Considering of the limitations of existing hardware sensors in quantitatively evaluating of rebar corrosion degree, a novel non-contact capacitive transducer (CT) as an alternative hardware sensor, which can directly determine the rust layer thickness, is being developed the first time for corrosion detecting. To help the design and experimental planning of the sensor, finite element methods are adopted to simulate the electric field distribution and to predict the capacitance outputs in the corrosion tests. In the simulation, a new corrosion process development model is built, and rust layer thickness growth hypotheses is raised for corrosion simulation. Corrosion simulations on various diameters of rebar with two different corrosion volume expansion ratios have been conducted. The simulation results have demonstrated that the developed capacitive sensor would be highly effective in measuring rust layer thickness of various rebar and the method is more sensitive for a larger diameter of rebar as well as a higher volume expansion ratio. The simulation has also been successfully conducted in both uniform and non-uniform corrosion tests of reinforced concrete for the sensor and the results have shown that the performance of the sensor could be quite promising. The simulation works provide theoretical base for such direct CT sensing method development, which can lead to a promising corrosion monitoring sensor networks in future to provide useful information for safety operation of civil infrastructures.