Is it okay to end the invention patent in a big factory and only pay the utility model patent?

You can't. According to the query of China Science Network, the invention patent of Dachuang did not exist before the utility model patent was rejected. Therefore, the device structure and utility model patent should be submitted at the same time, so that the utility model patent can be authorized first. Therefore, the invention patent of Dachuang can not only be handed over to the utility model patent.