What do you mean? It should work on all computers, as long as you have both the Java IDE and greenfoot installed on the ones you use. It's java, so writing code on one computer works on all computers with java.
Make sure your paths are relative to the project directory rather than absolute - if you're using images for instance, put them in the image folder in your project folder and reference them from there.
If you're using absolute paths, then it becomes very difficult or impossible to make your application portable.