During boiler boosting of boiler, the working condition of boiler is changing too much, such as the combustion is not stable and the adjustment is frequent. After steam temperature and steam pressure are increased, the exhaust steam quantity is changing and regular drainage is carried out, etc., the change of these working conditions will have different impact on the water level in different degree, if the water level adjustment is not controlled properly, the water level accidents will be easily caused, therefore during pressure boosting of boiler, special attention shall be paid to the drum water level to the normal range.