I have a mpfi engine car. I've got checked all the feul injectors, the pump, oil filter, air filter, and spark plugs. Which all are in right shape and have no problem but still I am facing a problem of low milage just half of what other cars give. What could be the reason for the same??

1. Check engine timing with a timing light.
2. Replace oxygen sensor. A bad oxygen sensor can radically affect gas mileage, since it controls fuel injector duration.
3. Go over the whole ignition system. Check/replace spark plugs (NGK only), spark plug wires, rotor, distributor cap.
4. Replace air filter and fuel filter.
5. Check tire pressure.
6. Add Shell Regane or Chevron Techron fuel injector cleaner to your gas tank every 6 months.
7. Use 5W-30 synthetic engine oil (e.g. Mobil 1) and synthetic transmission fluid.
8. Check for any codes being thrown.

Oh, I would say check the computer for a code. And if you are to lazy for that I would say, your timing jumped a tooth, and then I would say spend the $18 and get a new O2 sensor. Or you might just need to give your injectors and throttlebody some additive and clean them.

How 'bout draging brakes, low tire pressures, alignment, slipping clutch? Something that makes the engine work harder to get in motion! Fuel quality? Try good brands and record the milage figures. Stay away from hi-octane unless you require that.
Winter blend fuels and cold weather driving lower gas milage figures anyway. It's a fact! My 4.7L V8 gets 40 miles per tankfull LESS every winter compared to summer with A/C on. Go figure. :-/