The invention relates to the field of high-strength single-crystal high temperature alloys and especially provides a fourth-generation single-crystal high temperature alloy with high strength and a stable structure and a preparation method thereof. The alloy is mainly applicable to aero-engine blade materials used at a temperature higher than 1100 DEG C. Chemical components of the alloy comprise, by weight, 3 to 5% of Cr, 5 to 12% of Co, 6 to 8% of W, 0.1 to 2% of Mo, 4.5 to 6% of Re, 2 to 4% of Ru, 5.5 to 6.5% of Al and 6 to 10% of Ta, with the balance being Ni. The preparation method comprises the following steps: preparing a single-crystal blade or test rod under the conditions that temperature gradient of a single crystal growth furnace is in a range of 40 K / cm to 80 K / cm, casting temperature is 1480 to 1550 DEG C, shuttering temperature is consistent with the casting temperature and a growth rate is 4 to 8 mm / min; and then carrying out solid solution homogenization treatment, high temperature aging treatment and low temperature aging treatment so as to allow the alloy provided by the invention to have high endurance strength. The alloy has a life of no less than 100 h in endurance conditions of a temperature of 1140 DEG C and a pressure of 137 MPa and has endurance strength equivalent to the endurance strength of an EPM102 alloy; and the alloy has the advantages of good structure stability at a high temperature, a wide heat treatment window and easily controllable solid solution treatment.