This paper deals with the electronic stability method for antenna array of shipborne 3D radar with mechanical scanning in azimuth and electronic scanning in elevation. Through analysis and calculation, it is proved that airspace missing in 3D radar using electronic stability method will not occur in most situations. The computing methods for several key parameters are provided in designing the 3D radar with electronic stability antenna, including computation of maximum phased-array angle in elevation, computation of phased-array angle for beam pointing horizontal plane in elevation, computation of beam digital required by electronic scanning in elevation, computation of elevation angle for radar, etc.il.