This paper describes the simple formula giving the dose rate in water around linear radioactive source. The formula was based on modified Sivert's formula. The calculated value was compared with several author's datas or experimental value, the results were as follows : 1) the maximum error between the calculated dose rate for ^<226>Ra source and Uchiyama's date was less than 10 percent. 2) agreement between calculated and measured attenuation curves with distance from Ra source was seen to be similar in Shape.3) agreement between the calculated dose distribution around ^<137>Cs source and Klvenhagen's data was seen to be similar.