In this paper,we reported a multiwavelength passively Q-switched Yb~(3+):GdAl_3(BO_3)_4 solid-state laser with topological insulator Bi_2Te_3 as a saturable absorber(SA) for the first time,to the best of our knowledge.Bi_2Te_3 nanosheets were prepared by the facile solvothermal method.The influence of three Bi_2Te_3 densities on the laser operation was compared.The maximum average output power was up to 57 mW with a pulse energy of 511.7 nJ.The shortest pulsewidth was measured to be 370 ns with 110 kHz pulse repetition rate and 40 mW average power.The laser operated at three wavelengths simultaneously at 1043.7,1045.3,and 1046.2 nm,of which the frequency differences were within the terahertz wave band.Our work suggests that solvothermal synthesized Bi_2Te_3 is a promising SA for simultaneously multiwavelength laser operation. In this paper, we reported a multiwavelength passively Q-switched Yb ~ (3 +): GdAl_3 (BO_3) _4 solid-state laser with topological insulator Bi_2Te_3 as a saturable absorber (SA) for the first time, to the best of our knowledge .Bi_2Te_3 nanosheets were prepared by the facile solvothermal method. The influence of three Bi_2Te_3 densities on the laser operation was compared to the maximum average output power was up to 57 mW with a pulse energy of 511.7 nJ. The shortest pulse width was measured to be 370 ns with 110 kHz pulse repetition rate and 40 mW average power. The laser operation at three infrared spots at 1043.7, 1045.3, and 1046.2 nm, of which the frequency differences were within the terahertz wave band. Our work suggests that solvothermal synthesized Bi_2Te_3 is a promising SA for simultaneously multiwavelength laser operation.