Established and designed the fourth order Hilbert fractal antenna model which is a kind of Signal acquisition device for transformer partial discharge UHF signal in order to Get better characteristics. Firstly, analysis the effect of the three kind of wire segments of the fractal antenna in the signal acquisition process, and established the antenna model based on HFSS in wire segments unit. The length of the three conductors, dielectric thickness, dielectric constant, line-width and other parameters have been optimized. As the results shown, there are four resonant frequency in the 0.3GHz-3GHz UHF range. The first pass band is than 500MHz widened in 0.3GHz-1GHz range. The other three pass band is also more than 450MHz in 1GHz-3GHz range. The gain parameter also has been improved as well as directionality. The antenna characteristics has been proved to meet the requirements through a vector network analyzer. The length of the fourth order Hilbert fractal antenna has been reduced, so it can be placed in the oil-immersed transformer cabinets for PD ultrahigh frequency signal acquisition.