Our current understanding of the charge distribution in thunderclouds is described by a simple tripolar model but it cannot well cover the variety of the charge structure drive by the complicated dynamic processes. Therefore, the in-situ measurements of the electric field in and above thundercloud become very challenging but essential. To explore the charge distribution in thundercloud, a sounding balloon carried with an electric field meter was used to measure the strength of the vertical electric field. In this work, the circuit of electric field meter was redesigned including the enhancement of the structure, the improvement of the connection to amplify the dynamic range of the electric field measurement and to promote assembly efficiency. The electric field calibration cage, which is also redesigned to improve its accuracy and safety for the calibration work, and external AC noise was also reduced by a better shielding design. In addition, a simple symmetrical cylinder model developed by Chuang  was applied to evaluate the altitude, depth, radius, and charge amount of the charge layers, and experiment results can help us reveal the detail charge distribution in thundercloud. Four flight experiments have been done in June 2016 and 2017, the rainy season in Taiwan, by joining a campaign organized by TTFRI. Three of the flight successfully flew into the convective cloud. In the flight experiment on 2016/06/05, four major layers of electric charge were identified. Each layer consists of multiple thin charge layers with different electric polarity, and commonly thin negative charge layer always on the top. Furthermore, the polarities of the total charge in these layers were all recognized as positive. The second and third flight experiment on 2017/06/02 experienced a strong electric field, greater than 600V/m, and even damaged the electric field meter and aviation electronics. The experiment results also indicated that the electrification process of raindrop is complicated, and need more flight experiments to explore.