The invention relates to a system and a method for adjusting pressure of a heat supply pipe. A heat supply pipe at high temperature and high pressure and with long routing distance and great height difference is divided into a plurality of pipe sections according to elevations, water turbines are installed on a certain or a plurality of pipe sections which need to be depressurized; the inflow pipe of each water turbine is connected with an upstream pipe section of the pipe section and the outflow pipe of each water turbine is connected with a downstream pipe section of the pipe section; an auxiliary water pump is installed on another pipe section opposite to each water turbine, the inflow pipe of the auxiliary water pump is connected with the upstream pipe section of the another pipe section and the outflow pipe of the auxiliary water pump is connected with the downstream pipe section of the another pipe section; the rotating shaft of each water turbine is in power connection with the rotating shaft of the corresponding auxiliary water pump. By converting potential energy into mechanical energy, driving the auxiliary pumps to operate and decreasing the downstream operating pressure by using the water turbines at the same time, not only can the pressure adjustment flexibility, and the safety and the reachability of the heat supply pipe be greatly improved and can the increased initial investment and heat supply energy consumption for solving the problem of overpressure be reduced, but also the electric energy consumption during transportation of primary network return water is reduced and the goals of recycling waste energy and increasing economic benefits are achieved.