A high-refraction low-dispersion optical glass with refractive index of 1.77-1.85 and Abbe number of 40-48, includes the following components by mole percentage: 5-25% of SiO2, 15-45% of B2O3, 5-25% of La2O3, 1-20% of Gd2O3, 0-10% of Y2O3, 0-8% of TiO2, 0-8% of Ta2O5, more than 0 but less than or equal to 8% of Nb2O5, more than 0 but less than or equal to 15% of ZrO2, 18-40% of ZnO and 0.28-1.2 of SiO2/B2O3. The invention reduces the content of Ta2O5 and optimizes the cost of raw materials. Through rational composition design, the optical glass of the invention is conducive to precision molding while achieving the required optical constant, with excellent chemical stability. A glass preform and an optical element made of the optical glass are also disclosed.