Purpose: Low back pain is one of the most common health problems of the world. Very different causes can cause back pain. Approximately 85% of people who are examined for low back pain the cause is not specific. The purpose of this study is to investigate the effects of the knee abnormalities on pain intensity and functional fitness in middle aged men with the chronic nonspecific low back pain. Method: The statistical community of this study includes 30 people of patient’s male with nonspecific chronic low back pain in the age range of 30-50 years with one of the abnormalities of genu varum or genu valgum. Results: The research findings were analyzed using descriptive and inferential statistical methods (dependent t and independent t tests). The research findings indicate that both the pain and disability of the experimental groups have significantly decreased after applying selected of corrective programs (Stretching muscles and short elements and strengthening weakened muscles). Sitting frog, walking with the inner edges of the legs, pressure to enter the wall with the outer edges of the legs to modify the genu varum. passing legs from one side to another in the form of scissors in liner mode, passing the medicine ball to the wall with the inside of the legs, walking with the outer edges of the legs to modify the genu valgum (p<0.05). While the two variables in the control group did not differ significantly (p>0.05). Conclusions: According to the results and considering the conditions prevailing on the research samples, it can be concluded that knee abnormalities (genu varum and genu valgum) affected by pain intensity and functional fitness efficacy in nonspecific chronic low back pain patients and Corrective exercises of these abnormalities has had a significant effect on reduce pain and disability index.