Why is my orchid's leave falling off and stem are turning soft?

Sounds like bacterial or fungal rot to me. It's probably going to die, but it's possible to save it. Cut off the soft part with a sterile single edge razor, it might come back from the base. Dust the cut edge with sulfur or some other fungicide to keep the rot from coming back. And to prevent it from happening to your next orchid, don't let water collect anywhere on the plant--if water pools on the leaves or worse at the base of the leaves, stuff could start growing in the water and cause rot again.

A picture would really help, though. Not positive if it's really rot. But from my orchid experience, I'm pretty sure it's rot.

Why is my orchid's leave falling off and stem are turning soft?
You're overwatering them, and possibly over-fertilizing as well, and they may also be in an area that doesn't get enough air circulation. Cut back on the water and fertilizer. They should be planted in loose bark, rather than soil; their roots need LOTS of air (most orchids are essentially epiphytes), so if they're in soil, I'd suggest getting some bark-type potting mix for them and repotting them. Good luck!
Reply:probably over watering it
Reply:It is probably buried too deep in potting soil, with no air flow to the roots, and TOO MUCH WATER.

Owners who over love/water their plants are the worst culprits of early plant death.

Go to a web site and read about the needs of your particular orchid! Good luck, and Good reading!