Abstract: Round baler has advantages of simple structure，low failure rate and easy maintenance.Disadvantage is that during operation of round baler，materials in bale chamber increase，and pressure in bale forming chamber increases gradually.Under action of pressure，rear bin appears a certain opening phenomenon and resulting in decrease of bale density and poor bale forming effect.Combined with structure of round baler，bundling principle of materials in bundling chamber of round baler was analyzed.Structure and hydraulic control mode of bundling chamber of round baler by using TRIZ contradiction matrix and innovation principle were improved.Two improvement schemes for increasing bale density of materials were put forward.And optimal scheme was selected through analysis for experimental verification.Test results showed that bale density was increased from 117.6 kg/m3 to 159.0 kg/m3，and improvement effect was obvious.