Ms Pelosi left on Wednesday after a brief but controversial visit to Taiwan, which China regards as a breakaway province.
In response, China announced five days of "necessary and just" military drills, which will begin on Thursday.
Taiwan said 27 Chinese warplanes had already entered its air defence zone.
On Wednesday, Taiwan's defence ministry said it had scrambled jets to warn them off.
China has said the exercises will take place in some of the world's busiest waterways and will include "long-range live ammunition shooting".