The numerical analysis of thermal elastohydrodynamic lubrication for modified involute helical gear was carried out by using the mathematical finite line contact model of gear engagement.The thermal elastohydrodynamic lubrication of modified involute helical gear with positive,negative and equal displacement coefficients was analyzed.The pressure profile,film thickness and oil temperature rise of modified involute helical gear were calculated,and the results were compared with the results of the standard gear transmission.The results show that under thermal elastohydrodynamic lubrication conditions,the modification of the helical gear has little effect on the oil film pressure and has obvious effect on oil film thickness.The oil film pressure is decreased and film thickness is increased with the increase of positive modification coefficient of the driven gear.Along the longest contact line,compared with the standard transmission,the modified involute helical gear has the minimum pressure,the maximum film thickness and the lowest temperature under the positive modification coefficient.So the selection of positive modification coefficient is more conducive to lubrication of the helical gear.