原地址：http://game.ceeger.com/Manual/HOWTO-FixZAxisIsUp.html
Some 3D art packages export their models so that the z-axis faces upward. Most of the standard scripts in Unity assume that the y-axis represents up in your 3D world. It is usually easier to fix the rotation in Unity than to modify the scripts to make things fit.
一些3D制作包导出的模型是Z轴向上的，在Unity中大多数标准脚本，假设Y轴在3D世界中表示向上的。在Unity中非常容易修正旋转而不用修改脚本。
Your model with z-axis points upwards 你的模型是Z轴向上
If at all possible it is recommended that you fix the model in your 3D modelling application to have the y-axis face upwards before exporting.
如果有可能，建议你在导出前在3D建模软件中修正模型以便使Y轴向上。
If this is not possible, you can fix it in Unity by adding an extra parent transform:
如果做不到这一点，你可以在Unity中添加额外的父变换来修正它。
- Create an empty GameObject using the GameObject->Create Empty menu
使用GameObject->Create Empty菜单创建一个空的GameObject(游戏物体) - Position the new GameObject so that it is at the center of your mesh or whichever point you want your object to rotate around.
定位这个新的游戏对象，使他位于网格的中心或者想要物体围绕旋转的点上 - Drag the mesh onto the empty GameObject
拖拽网格到这个空的游戏对象上
You have now made your mesh a Child of an empty GameObject with the correct orientation. Whenever writing scripts that make use of the y-axis as up, attach them to the Parent empty GameObject.
现在你已经将网格作为一个具有正确方向的游戏对象的子物体了，写脚本的时候使用Y轴向上，并将他们附加给这个空的父物体上。
The model with an extra empty transform 带有一个额外空变换的模型