When your first construction certificate and second construction certificate are the same major, you can't use them at the same time. When obtaining certificates of different grades in the same major at the same time, you must cancel the registration of the second construction project before you can register the first construction project. For example, if you have obtained the first-class and second-class certificates of highway construction at the same time, then your second-class certificate must be cancelled at this time. Otherwise, when registering, the competent construction department will find that the certificate is duplicate and will not pass the registration.