Abstract: Aiming at the problems of mechanical vibration and lifting block caused by the interference of casing expansion and cylinder lifting motion during the operation of cotton topping machine, a solution of coaxial vertical installation and elastic connection between hydraulic cylinder and cutter shaft is proposed. 3MDZ-18 hydraulic driven cotton topping machine was designed and developed. The field test results showed that when the operating speed was 3.45 km/h and the cutting knife speed was 800 r/min, the topping rate reached 90.50%, and the qualified rate of topping length was 85.33%. The topping machine had no lifting stuck and rigid impact, and the stability and topping accuracy were improved to some extent.