This article is also for projects with non-gradle build, there are some differences in gradle build. It's easy to reference other engineering libraries in eclipse, but it's a little bit more complicated in Android studio. How to cite other projects as the library of the project, first you want to refer to the project as a module in the form of import. How to import module, see this article:how Android Studio Import module (for non-gradle)
After the project import into module, the specific operation look at the picture:
Similarly, open project structure, click on the module you want to use as the library, then click Android, and in the right frame, before the library module √.
Select the module you want to refer to, such as the Red box button.
In the popup dialog box, select the library module you want to refer to (there will be several module on this side depending on how many module you have set to Lirary module)
Click OK, you can see the Export box appears in the library module you introduced, select the Library module, and then Apply,ok.
How Android Studio adds Engineering (project) to the library (for non-gradle)