I had a knee replacement 6 years ago it get stiff pain movement get bad?

Needs evaluation. Some knees never attain full range of motion after replacement. However, your knee should be evaluated to insure that there is no issue such as loosening of the parts or chronic infection.
Stiff TKA. Consider checking with your operating orthopedic surgeon for x-ray and exam. Check for contractures, synovitis, loosening, or infection.