The invention discloses a safe and energy-saving immovable-string viscosity-breaking and paraffin-inhibiting system, which is applicable to offshore oilfields. The system comprises a water heating part, a water filling part, a downhole coaxial string part and a control part, wherein the water heating part adopts a heat pump machine set; the downhole coaxial string part comprises a coiled tubing string and a thermal-insulating pipe, and the coiled tubing string is arranged in an oil pipe; the coiled tubing string comprises a check valve, an intra-pipe packer, an intra-pipe safety valve and a coiled tubing which are sequentially connected from top to bottom; the thermal-insulating pipe is arranged in the coiled tubing, and a high-temperature water circulating annulus is formed by the thermal-insulating pipe and the coiled tubing; an oil extraction annulus formed by the coiled tubing and an oil pipe is communicated with an outlet of the safety valve in the pipe; high-temperature water of the heating part enters into the upper end of the thermal-insulating pipe through the filling part, the high-temperature water after being performed circulating heat release by the annulus is changed into low-temperature water, and then the low-temperature water enters into the heating part; and the control part controls the pressure of the circulating water so as to open the safety valve in the pipe and establish an oil extraction channel, and then a viscosity breaking and paraffin inhibiting effect on extracted crude oil is achieved through controlling the temperature of the circulating water. The system disclosed by the invention is safe and energy-saving, and can be applicable to offshore oilfields.