A leakage model of water supply plastic pipes was constructed based on the mechanism of leak area variation with pressure delay in the viscoelastic theory of plastic material and the orifice outflow model in order to accurately simulate the physical leakage flow of plastic pipes in urban water supply network. The leakage model of water supply plastic pipes is related to the pipe material, pipe inside pressure, leakage area and time. A discretionary pressure management method was proposed by imitating the discretion in the field of economics in order to select a more appropriate pressure regulation strategy and achieve more refined pressure management. The particle swarm optimization algorithm was written by MATLAB, and the pressure-driven hydraulic analysis function of EPANET 2.2 was called in order to solve the leakage model of water supply plastic pipes. Then the optimal setting value of pressure-reducing valve outlet pressure was obtained at each moment, and the discretionary pressure management strategy was developed. Pressure management experiments were conducted in a community located in the southern coastal area by using the traditional pressure management scheme and the discretionary pressure management scheme, respectively. Results showed that the leakage rate of this community was reduced by 56.0% after using the discretionary pressure management scheme, which is better than the traditional pressure management scheme. The reasonableness and feasibility of developing a discretionary pressure management strategy based on the leakage model of water supply plastic pipes was verified.