Application of phased array technology to detecting atmosphere is a new subject. By using the data of phased array weather radar and Doppler weather radar, both obtained from a severe tornado and a squall line on 30 May and 2 June 2004 respectively, the radial detection precision, tangential detection precision, scanning time, sensitivity, and reflectivity, r adial velocity, the life time of supercell were compared to investigate their detecting abilit y and detecting precision. Results show that detection precision of phased array radar will change with the changes of scanning direction angle because of the c hanges of phase scanning antenna beam width. Detection precision of Doppler weat her radar will have a little change at the whole scanning coverage. Tangential r esolution of phased array radar is lower than that of Doppler radar. In order to improve its resolution and reduce the scanning time, an effective scanning meth od of phased array radar is provided, which uses a transmitted wider beam in pit ch and narrower in azimuth, and multi received beams to overlap transmitted beam . This scanning method can largely reduce scanning time, improve reflectivity si gnatures and detect the evolution of severe storm in detail. A simple dealiasing velocity ambiguity method can also eliminate the ambiguity of velocity from be am multiplexing scanning.