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Internal combustion Rankine cycle (ICRC) with oxyfuel is a novel concept to achieve zero carbon emission in theory due to the carbon dioxide capture system, and nitrogen oxides can be completely eliminated as intake of air is replaced by oxygen. In previous studies, traditional compression ignition engine coupled with ICRC system (CI-ICRC) shows great potential in brake thermal efficiency (BTE), emission characteristics and cycle performance through direct water injection (DWI). Since the CI-ICRC has been proved a feasible way to realize high efficiency and low emissions, a selfdesigned CI-ICRC prototype engines was established, series of experiments have been conducted focusing on the optimization of CI-ICRC engine including oxygen content, DWI temperature, DWI timing, etc. In this study, to further determine optimum DWI strategy, the effect of DWI pressure on cycle performance and emissions characteristics has been investigate. According to experimental results, under 320℃A DWI timing and constant mass of injected water, higher DWI pressure with shorter DWI pulse width reduces the direct impact of vapor on combustion so that shorter ignition delay and less HC emissions are obtained. With the increase of DWI pressure, the cycle performance and BTE of CI-ICRC prototype engine is improved due to the better atomization of water. The optimum BTE achieved within the prototype engine is 46.6%, with coefficient of variation close to 1% under 35MPa DWI pressure. But the NO X and soot emissions slightly increased as elevating DWI pressure. The experimental results can also be utilized in providing reference information for DWI utilization within other novel internal combustion engine concepts.