I replaced all parts inside toilet tank. Water keeps going down,but not leaking on floor.Don't see water leaking no where. What could be wroung?

Flapper valve at the bottom isn't sealing... run your finger along the edge of the seat area along with the rubber flappers and make sure its both clean and smooth.

Put some food coloring in the tank and look at th bowl in 5 minutes. Colored? Leaking flapper, possibly the wrong one. What brand toilet?

"all parts inside toilet tank" including the flapper and its seat? Why did you replace these parts, what was the initial problem that caused you to replace anything?

Water keeps going down,A few things could cause this problem.
1- The flapper linkage is too tight.
2- You failed to cut the ring off the flapper, (see image) **or**
3- As Brian pointed out you may have a bad seat on the flush valve.
Good luck, Tom