The invention provides a preparation method of rare earth-doped gadolinium oxysulfide and oxygen-containing gadolinium sulphate up-conversion phosphor, and belongs to the field of material science. The method comprises the following steps that 1, Gd(NO3)3.6H2O, Yb(NO3)3.6H2O and Ln(NO3)3.6H2O are mixed, deionized water is added, and a RE(NO3)3 solution is obtained; 2, ammonium sulfate is dissolved into the RE(NO3)3 solution, stirring is conducted, stirring continues, ammonia water is added, the pH value is regulated, and suspension is obtained; 3, the suspension is subjected to a hydrothermal reaction for 1-72 h at the temperature of 100 DEG C to 150 DEG C and then naturally cooled to room temperature, and a reaction product is obtained; 4, the reaction product is centrifugally separated, washed and dried, and a white powder precursor is obtained; 5, the white powder precursor is calcined, and the rare earth ion-doped Gd2O2S or Gd2O2SO4 up-conversion phosphor is obtained. According to the method, the problems of usage of sulfur-containing raw materials and discharge of harmful by-products in a conventional method are effectively solved, and the method is a green and environment-friendly preparation technique.