Abstract: The invention relates to electrical engineering, in particular, to the manufacturing technology of flexible high-temperature superconductors (HTS) with high critical current density in external magnetic field and to the method of manufacturing of said superconductors (tapes). The invention is applicable to industrial manufacturing of HTS wires with very high values of critical current density in magnetic fields over 1 Tesla at temperatures below 50 Kelvin, in particular, to industrial manufacturing of HTS wires intended for application in compact fusion reactors. Flexible high temperature superconductor is comprised of a substrate and a superconductor layer with RE1+2xBa2Cu3O7+3x overall composition comprised of a superconductor matrix of REBa2Cu3O7 composition and non-superconducting nanoparticles of RE2O3 composition, where x=0.05-0.15, RE is a rare earth element from the Y, Dy, Ho, Er, Tm, Yb and Lu group, whereas the concentration density of the said nanoparticles is at least 1016 nanoparticles/cm3.