What is best way to block amobile home? Where I live in this park Ihave low spot where I live. Ihave plastic on the ground .But the house moves lot in winter time

Depends on whether the wet ground is because it is in a sump (surface drainage collects there) or it is swampy ground that is constantly fed by underground springs, water table etc. The plastic may be doing harm by preventing the ground from drying out, especially if the water arrives via surface runoff.
You may be able to increase stability by spreading the load out by increasing the area of the blocking, such as timber mats.
Some others here may have some other suggestions but generally speaking it is very expensive to create stability on swampy or continually wet ground.
Assuming that it is accumulating because of surface water (rain)--is there any way to divert that water by for instance redirecting a ditch line or by diverting some other obvious source of runoff? Good luck.