An image sensing apparatus and a black level controlling method thereof are provided. The black level controlling method includes following steps. A conversion relationship between analog gain values and offset values is provided. An analog gain value is converted into an analog offset value by using the conversion relationship between analog gain values and offset values. Whether to adjust the analog offset value is decided according to a first optical black data corresponding to a first part of optical black pixels. A digital data offset value is calculated according to a data corresponding a second part of optical black pixels.