In this paper, the relationship between design purposes, functions and structure parameters for vertical blade of boat tractor 1GMC-70 was analyzed. Mathematic equation of leading edge for the vertical blade was built.Vertical blade kinematics was analyzed by using software Matlab.The results show that the structure parameters of the vertical blade do not match well with its design intents.The effective cutting length of the vertical blade is less than one-third bite length of the helical blade,so its own cutting straw capability and the capability of helping helical blade to process straw are all weak.The vertical blade can break untilled soil in advance, but the cutting depth is only about one-third thickness of the helical blade′s furrow slice. Therefore,the effect of the vertical blade to break the untilled soil is small.The vertical blade can pulverize tilled soil clod behind rotor, but the effect is negligible. The vertical blade cuts only about 40% of the furrow slice′s cross sectional area,so its furrow slice breaking effect is small.The arrangement of vertical blades,which is 4-3-4-3-4,does not increase their own tillage opportunities.Field tests show that the existence of vertical blade has no impact on paddy field tillage quality.As a result, the vertical blade with current structure parameters does not achieve its design intents.It should be redesigned.