Abstract: In order to engineer the hybrid-connected ISD suspension, a design scheme was proposed in combination with hydraulic inerter and a hydro-pneumatic spring. In allusion to the problem that the parasitic damping and the additional stiffness produced in engineering may worsen the suspension performance, a quarter vehicle dynamics mathematical model was built. The impact of the parasitic damping and the additional stiffness on the suspension performance was analyzed by the simulation, and a muti-objective optimization method was used to optimize the design of the parasitic damping and the additional stiffness. The results indicate that the low frequency peak value of the power spectral density of the body acceleration, the suspension working space, and the dynamic tyre load of the engineering hybrid-connected ISD suspension decrease respectively 1.6%, 3.9%, 1.1% compared with the hybrid-connected ISD suspension. And their RMS value decrease 12.2%, 11.4%, 8.6% compared with the hybrid-connected ISD suspension. Therefore, it is necessary to limit the parasitic damping and the additional stiffness to a reasonable range by optimization design to make the suspension performance essentially constant before and after engineering. The research can provide theoretical basis for the engineering design of the hybrid-connected ISD suspension.