A non-uniform model of the load per unit of length distribution of helical gear with modification and misalignment was proposed based on the meshing stiffness, transmission error, and load-balanced equation. The distribution of unit-line load, transmission error (TE), and contact press of any point on the contact plane were calculated by the numerical method. The feature coordinate system was put forward to implement the helical preliminary design and strength rating. The thermal elastohydrodynamic lubrication (EHL) model of helical gear was established, and the pressure, film, and temperature fields were obtained from the thermal EHL model. The maximum contact temperature and minimum film thickness solved by thermal EHL were applied to check the scuffing load capacity. The highest flash temperature and thinnest film occur in the dedendum of the pinion. The thermal EHL method to evaluate the scuffing load capacity is effective.