My car moves forward but when i shifted to backward, car doesn't move. I checked oil level, it's very less. Is replenishing the oil will solve the problem? Are there any reasons other than oil level?

It could be many things:
1. Automatic transmission oil level low.
2. The torque converter does not attach to the flywheel
3.Forward sprag not holding
4. Automatic transmission oil pressure low
Internal damages. Need to remove transmission apart.

Hope it helps.

Make sure the shift lever on the transmission is actually shifting the shaft that selects the gears.....Something is slipping where you installed the bushing.....Check for proper cable adjustment....Apply the E- Brake while working with cable to prevent accidental runaway........

Sounds like the shift cable is off the transmission under the hood. Raise the hood and check to see if the cable is moving the linkage going into the transmission when the shift lever is moved in the car. Be sure to have park brake on.

If the transmission will not move the car forward in Drive, check fluid level, fluid condition, transmission filter, and linkage adjustment.
If the transmission will move the car forward in Drive but will not shift out of First Gear, the shift governor has failed.

If the car won't move but you can hear the transmission shift gears, something has broken where the drive axle shafts connect to the transmission.

Have you checked the fluid levels in the transmission?

Well oil isnt transmission fluid, if the tranny fluid is low that could help cause the conditio but its most likely the B2 piston going out. The 2 pistons can be replaced while transmission is in the car its the best place to start.

check transmission fluid first.if its low add to get correct level.if transmission fluid look dark smells burnt replace fluid and filter.if car still dont move forward.looks like you have bad worn out forward clutch plates and seals.also bad transmission oil pump.you need a overhaul or new transmission.

it sounds like something broke inside the transmission

YOU HAVE BURNT THE FORWARD DRIVE CLUTCHES.THE TRANSMISSION NEEDS TO BE REBUILT.