In this paper the construction characteristic and the electron-optical character of the improved Henke ultrasoft X-ray source are presented. Many improvements on the basis of the Henke source have been done in the new improved one. For the first time the double cathodes and four focus lines stracture are adopted. The spatial distrubution of radiative intensity is effectively improved and flattened by the rational allocation of four focus lines. A new cathode (LaB

6

)takes the place of tungsten filement

which reduce input power and raises cathode emiting efficiency. In addition the target voltage formula of radiation intensity maximum is derived for the normal incidence of the electron beam. The characteristic line spectra of Alk

α

Cu-l

α1α2

B-k

α

and Be-k

α

are calculated by use of this formula. The calculation results accord with the Henke's measurment results.