I'd recommend taking a look at an app such as MinCart to set up maximum order limits. They are going to allow you to set up conditions centered around the customer, which appears to be what you are looking for. The app features a 7-day free trial and then starts at $2.99/month. If you need any help setting up the app, you can get in touch with the developers of the app by email here.
If there is anything else I can help you with, please let me know.
Thanks for your suggestion. I have try MinCart before. It seems that they didn't support multi - language. Our webpage have both English and Chinese. In the Chinese version, the pop up message cannot change to Chinese and the checkout button still allow customer checkout over the limitation. I have sent them this problem and waiting for reply. I a try to seeking another solution to reply this app.