The relationship between the belt tightness of walking tractor and power losses was researched through tests and theoretical analysis. The result showed that the loss of frictional power increases when the belt deflection decreases, while the loss of slipping power increases when the belt deflection increases. Taking these two aspects into accoumt, an optimal belt tightness was worked out, that is , when a force is added in the middle of the belt, the deflection of the belt should be within 25 mm～30 mm. In addition, a simple instrument was designed to inspect the belt tightness. Deflections of 121 belts of walking tractors in use were measured and analyzed. It was found that 60 percent of the belt tightness cant meet the requirement,so the adjustment is needed.