Abstract: An air core spiral strip transformer with 0.8 of coupling coefficient, which can operate in pulse high voltage, has been researched and manufactured .The experiments showed that output voltage of transformer rose up to about 500kV at an input 40kV. The elementary theoretical analysis of the transformer has been carried out . This kind of transformer has characteristic of compact construction, small volume and excellent electric performance. It has been used to charge of water Blumlein line of accelerator. In the vacuum diode of accelerator, high voltage pulse of 500kV, 40kA with 80ns (FWHM) has been obtained.