We arrive at Beijing T2 at 23.30 PM. How can we go to Tianjin without waiting until next day?

Train must be a good choice. Upon landing at PEK, you need 0.5-1 hour to check out. Then, you may take Night Bus Line 2 from PEK to Xidan Station for CNY 24. After that, take a taxi to South Railway Station, where trains to Tianjin are available almost around the clock, for about CNY25. The buses operate until the arrival of last domestic flight, so probably you can catch it. Or, you can take a taxi to the south railway station for about CNY 130.

Thank you very much Bob. Really appreciate.Thanks again.