Aiming at the problem that the existing chain-type paper pot seedling transplanters are mostly continuous chain transplanting with unadjustable plant spacing and cannot meet the requirements of large plant spacing crop transplanting, this paper explored and designed a seedling chain breaking device for chain pot seedling transplanters, taking conventional hexagonal cross-section chain pot seedlings as the test object. Based on the principle of seedling chain breaking device, the structure of key components and the value range of working parameters were determined through theoretical analysis of working process. A test bench was set up for single factor test, with the opening of the pinch finger, the inclination angle of the seedling chute and the planting frequency as the main test factors, and the success rate of seedling taking and the matrix loss rate as the evaluation indexes. The orthogonal combination test of three factors and three levels was carried out to analyze the influence of each factor on the evaluation index and optimize it. The test results showed that the effect was better when the opening of the pinch finger was 52mm, the inclination angle of the seedling chute was 20°, and the planting frequency was 45 plants/min. Under this parameter combination, the success rate of seedling taking was 91.3% and the matrix loss rate was 14.2% in the bench test, and the success rate of seedling taking was 87.5% and the matrix loss rate was 17.4% in the soil tank verification test. This study can provide reference for the development of the whole chain pot seedling transplanter.