Prism transmission type double-colored water level gauge used for steam boiler or other pressure container monitor once of water level read the instrument direct. It is on the basis of summarizing and producing the transmission type and reflecting type double- colored water level gauge both at home and abroad, concentrated the advantages of two kinds of water level gauge and developed. It is the characteristic that the volume is small , the weight is light, performance is reliable , install and safeguard conveniently , it is the ideal instrument which monitors the water level of the boiler.