Objective To primarily test the reliability and validity of the Kashin-Beck Disease (KBD) affected big joints function assessing system for adult Tibetans in Rangtang County. Method From June to July 2009, 142 KBD patients were investigated with the function assessing system in Rangtang County of Ngawa. Cronbach’s α coefficient was calculated to estimate internal consistency reliability. Pearson’s r for the correlation of the items with the total score of the scale was computed to test the internal validity. Principal component factor analysis with varimax rotation analysis was conducted to explore construct validity. Result Both the response and complete rates of the scale were 100%. The time for completing the scale was 7.8±3.4 minutes. Cronbach’s α was 0.857, which revealed satisfactory internal consistency reliability. Pearson correlation analysis revealed significant correlation between the scores of each item and the total score of the scale (Plt;0.05). Pearson’s r value of each item was more than 0.4, only except the items of “sitting with legs crossed” and “standing at attention”. The principal factor analysis extracted three latent factors explaining 68.1% of the variation together. The latent factors weights of the items were over 0.4 except the items of “standing at attention”, "taking food” and “wiping after defecation”. Conclusion The reliability and validity of KBD affected big joints function assessing system for adult Tibetans in Rangtang County was good in this primary test, the function assessing system has to be widely applied and further assessed among Tibetans suffered with KBD, in order to provide a standard evaluation criterion in KBD integrate control.