The insulation system of a transformer comprises solid Kraft paper insulation and liquid transformer oil. However, due to the continuous influence of thermal and electrical stresses, the insulation deteriorates. Two crucial degradation parameters that may be utilized to assess the age of the insulation system or the state of the transformer's health are 2-FAL (2-furfuraldehyde) and moisture. These parameters can predict the remaining life of the insulation of the transformer. In order to protect the transformer, continuous monitoring of the insulation system of the transformer is needed. This paper proposes a comb-type capacitive sensor for detecting moisture and 2-FAL concentration in oil. A simulation-based study is performed in Ansys Maxwell Software to analyze the feasibility and characteristics of the sensor in different sensing films. A silicon oxide and titanium dioxide film is used as a sensing film to increase the sensitivity of the sensor. Silicon Oxide (SiO2) and Titanium dioxide (TiO2) film show a good response for detecting moisture and 2-FAL in oil. The proposed sensor is a simple, low-cost, and effective method of online monitoring of transformer insulation health.