Taken a domestic first newly-built rail car roro carrier as an example, the design and arrangement optimization scheme of roro space water spraying system is implemented. The optimization scheme is introduced in detail from the design aspects of principle, division zone, standby/ redundancy, intelligent remote control, nozzle arrangement and partition main pipe arrangement, etc. By comparison with the design scheme of the basic designed roro space water spraying system, the optimization scheme possesses many advantages, such as reducing the number of pumps, optimizing pump parameters, solving the problem of the blind area of spraying in the adjacent area, reducing the consumption of pipe, greatly reducing the amount of construction. The function of optimization scheme is reasonable and feasible with the real ship test, and it can provide valuable reference for the design/construction of the roro space water spraying system for future ships or similar ships.