Abstract: A throttling cavitation venturi is one of the key components of the space variable-thrust liquid rocket engine. In order to reduce its pressure loss and improve its pressure recovery characteristics, a cylindrical segment is designed to be inserted in the venturi throat.Based on the experimental results obtained from the cold flow tests, the empiricalformula is proposed for the pressure recovery characteristics of the throttlingcavitation venturi. Through the theoretical analysis, the procedure for designingthe length of the cylindrical segment in the range studied and the availableinterval for choosing are presented. The analytical expression for the functionof venturi taper stroke H versus stroke difference Φ, maximum relativeerror ξ and throttling ratio E is derived. With the aid of correction factor λ, the value of the cylindrical segment length for ξ≠0 can be calculated from that for ξ = 0. The related graphics are also given. It is found that the throttling ratio E has a pronounced effect on the determination of the cylindrical segment length.