The problem occured to me after the update6.I’m now at the high-end graphics setting. When I enter the game,the fps of the game is pretty high,and there is no shuttering whatsoever.However,after about half an hour time of flying.The fps just doomed immediately,with a lot of shuttering.has anyone face a similar situation to me?
If you’re using ‘offline AI’ traffic settings, switch that to ‘live traffic’. There is an issue where offline AI generated aircraft don’t seem to despawn.
I’d suggest you download something like HWiNFO. This will let you check how your hardware is performing. For example, you can monitor the temp on each processor core, and gpu, and also the frequency of each in realtime. It sounds like after 30 mins of play your machine finally hits a thermal limit and slows your machine down to prevent damage.
My first thought was the AI traffic like MortThe2nd suggested, but that problem causes a slow steady degradation in performance not a sudden drop.
I’ve never heard anyone else complain of a sudden drop in performance so you are going to have to diagnose your problem with software like I suggested. Be sure to monitor the frequency for all of your CPU cores and GPU before and after the problem starts.
Yeah,I’m sorry that I explained it in the wrong words because it was so late in the night 
It is a gradually slowdown,now I’d like to try his idea 
I do currently using the live traffic mode,but I select the"All Players"mode.Would this be any damage?
Any type of AI traffic, live or not, slowly reduces performance right now. The game spawns in aircraft close to the player, but doesn’t remove that traffic as it gets far away from the player. Therefore, over time the number of AI aircraft increases. This has been shown to increase to hundreds of aircraft the game needs to keep track of and move around.
So the only way now would be flying in live mode?Will all players mode help?