Based on the design concept of 2BMFJ series no-tillage precision planter, which is light weight and uniform in sowing depth, a two-degree-of-freedom combined profiling no-tillage precision drill unit was designed. Based on Lagrange equation, a mathematical model of ditching depth of precision drill unit was established, and the key structure and working parameters affecting the ditching depth were determined. The autumn untreated maize stubble field was selected as the test plot. Four-factor and five-level quadratic regression orthogonal rotation center combination test method was applied, experimental optimization on structure and working parameters affecting the performance of precision drill unit was done, and the initial increment of spring, initial traction angle, spring stiffness and working speed were selected as influencing factors. The qualified rate of ditching depth, soil hardness and variation coefficient of ditching depth were selected as evaluation indexes, the primary and secondary relations of factors affecting the qualified rate of ditching depth were obtained as follows: spring stiffness, working speed, initial increment of spring and initial traction angle, the primary and secondary order of factors affecting qualified rate of soil hardness were as follows: spring stiffness, working speed, initial traction angle and initial increment of spring，and the primary and secondary order of the factors affecting the variation coefficient of ditching depth were follows: initial traction angle, working speed, spring stiffness and initial increment of spring. Design-Expert 6.0.10 software was used to establish regression equation, significance and optimization parameters of the test data were tested, the results showed that under the conditions of initial traction angle of 0°, spring stiffness of 10N/mm, initial spring increment of 15～19.5mm and working speed of 6.7～7.8km/h, the qualified rate of ditching depth was more than 95%, the qualified rate of soil hardness was more than 95%，and the variation coefficient of ditching depth was less than 10%.