Will the weather OK for travel to Beijing in late August? Any preparation needed?

Yes, it will. Generally, the temperature in late Aug. may drop a little, so it would be a little cool in the early morning or at night, while may also be hot in the afternoon, with the highest temp of around 31℃. Sunny days would mostly happen together with very rare thundershower. Then just pay close attention to the weather report before traveling.

I suggest you prepare summer clothes and light jeans and jacket.