Spur involute spline is the most typical and widely used type of spline in aeronautic transmission systems. Spur involute splines often suffer contact stress concentration due to angular misalignment. Such contact stress concentration phenomena may even further lead to serious local wear on spline teeth. Helical involute splines are considered by some scholars to be a potential type of spline to relieve contact stress concentration; however, the helical involute spline is far less investigated compared to the spur involute spline. In this paper, finite element models of both helical and spur involute splines are developed for contact stress prediction. Basic parameters, namely the helical angle and torque direction, of the helical involute spline are analyzed based on the developed finite element models. The results show that the presence of a helical angle causes non-linear changes in the contact stress of the spline, and does not optimize the contact stress concentration of the spur involute spline. As the helical angle increases, the contact area of the helical spline initially decreases and then increases, while the maximum contact stress value first increases and then decreases, with the location of maximum contact stress also shifting. In addition, the helical spline demonstrates sensitivity to misalignment that initially increases and then decreases.