Why import my own robot model goes to mess?

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I want to create my own robot model and simulate that with C or C++ code through gazebo. First I create my own robot model by Solidwork software and export the model to xml and STl files by using the plug-in SimMechanics Link. Then I transformed urdf fil from the xml file by the simmechanics_to_urdf packet. my code likes below:

rosrun simmechanics_to_urdf convert.py jixiebi.xml xml > jixiebi.urdf

After that, I copy all of the STL files to the catalog of /simulator_gazebo/gazebo_worlds/Media/models. Finally,I run the below code

rosrun gazebo spawn_model -file `pwd`/jixiebi.urdf -urdf -z 1 -model my_jixiebi

and now I can see my model. But the model goes to mess. I guess it's the coordinate error, but I don't know how to deal with. I know the urdf has origin tag but I find it's very difficult to fix all link's and joint's coordinate correctly. What's worse, my model has hundreds of links and joints. So, here is my questions.

1. Is there any wrongs in my process?
2. How to deal with my problem?
3. If the mess model problem could figure out, the next step is how to do?

Thanks a lot and look forward to your answer.