I had Honda Civic 98 Model, suddenly today It is not starting, Temp today is -8C. It has never given me starting problem.Battery seems to be OK.

Have you had any trouble starting when the outside temperatures were higher than -8, change your Engine Coolant Temperature (ECT or TW) sensor, it is a problem in many cases but my not be in your case, its not expensive.

Have you thought of putting a heater in one of your radiator hoses?

If it starts when it warms up you might throw some heet into the gas... water in the fuel freezing at the line maybe? I'm not a car guy... just something I've been told to do.

Be sure to use full synthetic engine oil; e.g. 5W-30 Mobil 1. Full synthetics are engineered for artic environments and will allow your engine to turn over much easier, making it less stressful on your battery and starter motor. Synthetics are the lubricants of choice for engines, transmissions, and differentials in cold climates.

If the problem persists, perform the tests in Sections A and B below:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-46563.html