Nitric oxide (NO) has significant influences on the infrared radiative transferring of hypersonic vehicle and its flow field, but the HITEMP database can calculate NO′s parameters only for 70 K~3000 K and at present the available algorithms for calculating NO′s partition function seldom take the effect of lambda-doubling in electronic ground into account. Therefore, calculation of NO′s radiative parameters with higher efficiency and accuracy is rather significant. According to the product approximation, the total internal partition function is decomposed into electronic, vibration and rotation partition functions. The fact that NO′s X2Π ground state splits into 2 spin components has been considered so as to improve the accuracy. With temperature between 3000 K and 8000 K, the rovibration partition function is rectified. Experiments show that the partition function of the proposed algorithm agrees with total internal partition sums (TIPS) of the HITEMP with temperature between 70 K and 3000 K, with the maximum error being no more than 0.3%. Moreover, the proposed algorithm can calculate partition functions under non local-thermal equilibrium. Besides when compared with the algorithms based on summation at high temperature as well as experiments, the proposed method has high accuracy.