In this paper, a new roll-plane hydraulically interconnected suspension (HIS) system is proposed to enhance the roll and lateral dynamics of a two-axle bus. It is well-known that the suspension tuning is of great importance in the design process and has also been explored in a number of studies, while only minimal efforts have been made for suspension tuning for the newly proposed HIS system especially considering lateral stability. This study aims to explore lateral dynamics and suspension tuning of a two-axle bus with HIS system, which could also provide valuable information for roll dynamics analysis. Based on a ten-DOFs lumped-mass full-car model of a bus either integrating transient mechanical-hydraulic model for HIS or the traditional suspension components, three newly promoted parameters of HIS system are defined and analyzed-namely the total roll stiffness (TRS), roll stiffness distribution ratio (RSDR) and roll-plane damping (RPD). Dynamic responses of the two kinds of vehicle model with Fishhook maneuver are obtained under a certain range of combination for the suspension parameters above. The responses are evaluated in terms of performance measures related to roll angle, yaw rate, trajectory, sideslip angle, lateral and longitudinal velocity of the vehicle. Additionally, the primary field test of Double-Lane-Change manoeuver is applied to validate the simulation work. Fundamental relationships between the vehicle responses and the proposed suspension parameters (TTS, RSDR, and RPD) are established, based on which some basic suspension tuning rules for buses with HIS system are also proposed.