The mechanism for the biradical reaction of HS with HO_{2} is investigated at the CCSD(T)/6-311++ G(3*df*, 2*pd*)//B3LYP/6-311+G(2*df*, 2*p*) level on both the singlet and triplet potential energy surfaces, along with rate constant calculations of the major channel.The results show that there are eight reaction channels involved in the HS+HO_{2} reaction system.The major channel R1 of the title reaction occurs on the triplet potential energy surfaces, and includes two pathways: Path 1 (R → ^{3}IM1 → ^{3}TS1 → P1(^{3}O_{2}+H_{2}S)) and Path 1a (R → ^{3}IM1a → ^{3}TS1a → P1(^{3}O_{2}+H_{2}S)).The rate constants *k*^{TST}, *k*^{CVT}, and *k*^{CVT/SCT} of Paths 1 and 1a for Channel R1 were evaluated using classical transition state theory (TST) and the canonical variational transition state theory (CVT), in which the small-curvature tunneling correction was included.The calculated results show that *k*^{TST}, *k*^{CVT}, and *k*^{CVT/SCT} of these two pathways decrease with rising temperature within the temperature range of 200-800 K.The variational effect was not negligible in the entire process of Path 1 and Path 1a, at the same time, the tunneling effect was considerable at lower temperature.The fitted three-parameter expressions of *k*^{CVT/SCT} for Paths 1 and 1a are *k*_{1}^{CVT/SCT}(200-800 K) = 1.54×10^{-5}*T*^{-2.70}exp(1154/*T*) cm^{3}·molecule^{-1}·s^{-1} and *k*_{1a}^{CVT/SCT} (200-800 K) = 5.82×10^{-8}*T*^{-1.84}exp(1388/T) cm^{3}·molecule^{-1}·s^{-1}, respectively.