Bad pixels in the area CCD detector are used as temperature sensor, to estimate the CCD temperature, and to establish the function model between the CCD temperature and the dark current. In order to make the result insensitive to noise; mean filtering method is used to estimate the CCD temperature in the image of the real scene. After extraction of the CCD temperature of the real scene, the dark current of area can be estimated. Based on analysis of the method, using the real dark current as standard, the result of the dark current estimation has been validated. The experiment shows that the estimation of the dark current is very exact in both different integration time and large dynamic range conditions with the rate of error under 0.4%. Furthermore, it is not sensitive to the noise within the images. The method uses the character of the image to estimate dark current, so it is not necessary to collect the dark-current data, and the image acquisition time can be saved. Therefore, this method is very suitable to the low-cost CCD imaging system without temperature control for real-time image acquisition in hyper-spectral imaging or astronomical observation fields.