I want to use unity3d to develop a app，when i export the model from sketchup ，iI found that the layer information was not exported，and now i want to export the model’s infos in a json file，but how？ Who did it，please help me
What export format did you use ?
Were the layers that failed to export empty of all entities ?
I do not know of any JSON exporter.
But there is a special exporter for game engines:
(Amazon Lumberyard, Crytek CryENGINE 3, Epic Games Unreal 4, and Unity.)