The background blackbody radiation causes the shift of the hyperfine energy level and affects the accuracy of the optical frequency standard. The polarizabilities of the hyperfine energy levels 5d106s2S1/2 (F=0) and 5d96s2 2D5/2 (F=2) of 199Hg+ are evaluated and the relative frequency shift at room temperature due to blackboby radiation is calculated to be -5.410-17. Finally the effect of blackbody radiation on single 199Hg+ optical frequency standard is discussed at an ultralow temperature.