Based on the theory of thermal elastohydrodynamic lubrication ( TEHL) ，the lubrication and friction characteristics of modified herringbone gears were analyzed． Firstly，the variation of instantaneous contact lines on tooth surface of the herringbone gears with the specified structure was analyzed under the specified working condition． The specified number of meshing points along the meshing line were selected as analysis objects and the essential values of contact parameters were obtained． Secondly，the accuracy of the TEHL calculation program was verified and the TEHL calculation was performed． The oil film characteristic values at the meshing points were derived from calculation results to obtain their variations along the meshing line． The influences of input torque， driving gear rotation speed and amount of crowned modification on the film profile curves at the meshing point S1 were analyzed． Finally，the variation law of the friction coefficients at the meshing points was obtained by using the Ｒee-Eyring model． The calculation results show that the maximum film pressure on tooth surface increases first and then decreases，while the variation trends of the minimum film thickness and the maximum film temperature are opposite to that of the maximum film pressure． In addition，the temperature rise and the thickness of the film are influenced significantly by the rotation speed of driving gear; the increase of input torque or amount of crowned modification will lead to the film temperature rise and the peak value rise of the film pressure; the value of friction coefficient is almost zero at the pitch point while greater at the engaging-in / out side．