Please be aware that Beijing and Bangkok has multiple airports and that these results are for all airports serving the city.
The best month to fly between Beijing and Bangkok is May and the most expensive month to fly is March. (Average prices, based on 241 datapoints.)
The best day to arrive at Beijing is Thursday and it would be best to avoid Saturday, as prices are on average 52.65% higher than on Thursday. (Average prices, based on 224 datapoints.)