Abstract: Straw is a good clean bio-resource in our country，and baled havesting of straws is a effective way to solve the problem of straws lack for the large-scale use. A new machine Model 9YDF-90 big baler was developed to meet the need of straw collection. And, performance experiments showed that the porperties such as rate of finished bale, rate of good bale and bale density of Model 9YDF-90 big baler can meet the need of baler standard. Furthermore, the relationship between bale density and compressing force of hydraulic system was linear, and the correlative coefficient was high.