Elderly people can improve knee joint osteoporosis through the following methods: First, maintain a balanced diet with plenty of calcium and vitamin D-rich foods such as milk, yogurt, and dark green vegetables. Second, appropriate exercise helps strengthen bones, like walking and light weight training, but avoid excessive weight-bearing exercises. Third, quit smoking and limit alcohol consumption, as these can affect bone health. Finally, regularly check bone density and consult a doctor to understand the bone condition, and take medications to enhance bone density if necessary under medical guidance.