The invention relates to an ultrahigh-
voltage flame-retardant 
electrolyte which comprises the following components in parts by weight: 65-75 parts of 
ethylene glycol, 5-10 parts of 
diethylene glycol,1-3 parts of nanoscale 
silicon dioxide, 2-3 parts of 
ammonium dodecanedioate, 3-5 parts of 
ammonium isosebacate, 3-8 parts of 
ammonium pentaborate, 3-5 parts of PVA-1179, 1-2 parts of o-nitroanisole and and 0.15-0.20 part of tributyl 
hypophosphite. The preparation method comprises the following steps: (1) firstly, mixing the 
ethylene glycol, the 
diethylene glycol, the 
ammonium pentaborate, the ammonium isodecanedioate and the PVA-1179, heating to 60-75 DEG C, keeping the temperature for 25 minutes and continuously stirring; (2) adding the ammonium 
dodecanedioate, heating to 145 DEG C, keepingthe temperature for 10 minutes, cooling to 70 DEG C, and keeping the temperature for 210 minutes; and (3) finally adding nanoscale 
silicon dioxide, uniformly stirring until the solution is transparent, preserving heat for 60 minutes, naturally cooling to 75 DEG C, adding o-nitroanisole and tributyl 
hypophosphite, and naturally cooling to normal temperature to obtain the 
electrolyte. The 
electrolyte is resistant to high temperature and 
high pressure, the amount of 
hydrogen generated in the working process of the 
electrolytic capacitor can be reduced, the electrolyte 
vapor pressure is reduced, and the 
flame-retardant effect is good.