［Purposes ］ The exhaust gas flow，shaft power，and exhaust temperature of Roots blowers were analyzed，focusing on those without countercurrent ports，those with horizontal countercurrent pipes on both sides of exhaust port，those with tangent countercurrent pipes with the base circle of rotors through center of both sides of casing，and those with long -strip countercurrent ports from pointing to the edge of the exhaust port on the same side of countercurrent port to pointing to the countercurrent port on the opposite side horizontally，so as to obtain the countercurrent port form that is beneficial for improving the performance of the Roots blower.［Methods］ Computational fluid dynamics （CFD） 2.5D dynamic grid technique was used to simulate the flow field of Roots blowers，and the exhaust gas flow，shaft power，and exhaust temperature were compared during one complete turn after the flow field stabilized，so as to compare the effects of each countercurrent cooling port on the performance of the Roots blower.［Findings］ On both sides of the exhaust port，long -strip countercurrent ports pointing to the edge of the exhaust port on the same side are arranged along the length of the casing.By utilizing the high-pressure countercurrent gas pointing to the exhaust port，it can directly impact and counteract the backflow of the exhaust gas when the exhaust port is opened，significantly reducing the exhaust pulsation of the Roots blower and lowering the exhaust temperature.Meanwhile，the high -pressure countercurrent gas flow can drive the rotor to rotate，thereby reducing the rotor ’s shaft power.The Roots blower featuring long -strip countercurrent ports from pointing to the exhaust port has a 69.4% and 72.1% reduction in the fluctuation amplitude and unevenness of the exhaust gas flow compared to that with horizontal countercurrent pipes，as well as a 5.1% reduction in shaft power and a 9.0% decrease in exhaust temperature.The proximity of the countercurrent port to the exhaust port，as well as the larger intersection area between the long -strip countercurrent port and the rotor blade peaks，can reduce the flow of high -pressure countercurrent gas entering the casing，thereby reducing the internal circulation flow caused by countercurrent.The flow rate is basically consistent with that of the Roots blower with horizontal countercurrent pipes.For the long -strip countercurrent port with same shape and position，when pointing from the edge of the exhaust outlet on the same side to horizontally pointing to the opposite countercurrent port，the shaft power and exhaust temperature of the Roots blower are basically the same，but the exhaust gas flow pulsation of the Roots blower with the countercurrent port pointing to the edge of the exhaust port on the same side is the smallest.［Conclusions ］ Roots blower with long -strip countercurrent ports pointing to the exhaust port edge on the same side can reduce exhaust gas flow pulsation，shaft power of rotors，and exhaust temperature compared with that with countercurrent pipes，and it has lower exhaust gas flow pulsation compared with other Roots blowers with countercurrent pipes which have the same shapes and positions.It has good engineering application value.