I have made an animated rigid body active character and the ground is passive rigid body. But the character's feet passes the ground that I don't want to happen.I want to move character so I don't want its feet sunken in the ground. I am a newbie so please explain in details.
It's going to happen any way you slice it. How you handle the slight annoyance is up to you. Option1 1. Use a floor constraint with an offset so whenever the floor is hit, it will not go through. https://docs.blender.org/manual/en/latest/animation/constraints/relationship/floor.html#:~:text=The%20Floor%20constraint%20allows%20you,ceiling%2C%20or%20a%20wall)!
Option 2. Use a solidify modifier so you don't see it go through . Real things have thickness. https://docs.blender.org/manual/en/latest/modeling/modifiers/generate/solidify.html
I tried a simple rigid body scene and the solidify modifier did a good job hiding, but this is part of the error in your simulation you will just have to account for in simulation. For actual manual animation, you can use the floor modifier with offset and that will work very well
If you're trying to animate a character that is to behave as normal, I don't think you want to try to use physics to solve problems with floor interaction. I personally don't know such an approach to be a recommended workflow in any 3D package. Floor collision difficulties are just something you are going to have to learn to deal with. One way to do it is by taking care when animating. If you simply ensure that all your foot keyframes are in the right position, and set in the correct order, no drifting through the floor plane will ever happen. For example, if you set the extreme forward and extreme back positions for an IK foot in a walk cycle, and do this before setting any other keyframes, then the foot has no choice but to slide straight back and forth between these two positions, and could be counted on to perform absolutely no movement along the vertical axis. Such an approach can be an essential foundation for all the keyframes which follow, as these two will ensure that no movement below the floor plane takes place.
Alternatively, you can use location constraints to help ensure that undesired behaviors never become possible, instead of relying on keyframes alone. But even here, care will have to be taken, particularly while setting up the character itself, so as to ensure that the bone positions of the armature properly meet with the floor plane at the same time that the character's foot geometry meets it.
Physics is a resource intensive operation. It is slow, prone to bugs, and not at all ideal for the purpose of general character rigging, in my opinion. It's certainly not a one-button alternative to planning your rig.