Traditional biopotential measurement methods such as Ag/AgCl electrodes are usually used to measure electromyography (EMG). However, they are not suitable for long-term biopotential measurements due to the risk of skin allergic reactions. In previous studies, capacitive electrodes was suggested to replace traditional electrodes to improve the above problems, but the friction with fabrics still generates 60 Hz interference and noise. Therefore, this paper proposes to use the capacitive electrodes and the noise suppression technology from Department of Photonics of Industrial Technology Research Institute (ITRI) to reduce the environmental noises and the noises generated from the friction with fabrics, so as to improve the quality of non-contact biopotential measurements. The size of the capacitive sensor has been tested and evaluated in skin-contact measurement and through-clothing measurement. The test results are that the Signal-to-noise ratio (SNR) can reach 59 db when using a sensor of $2\ \text{cm}\times 2.5\ \text{cm}$ in contact with the skin, and it can reach 35 db when using a sensor of $2\ \text{cm}\times 3\ \text{cm}$ through pure cotton clothing of 1mm thickness.