They said the manoeuvres, codenamed "Han Kuang (Han Glory) 20", would test the joint operations of the armed forces over a seven-month period. The drills are due to end in November.
"The objective of the exercises is trying to crush the enemy's attempt to wage a quick war," said Li Chieh-chia, joint operations head at the deputy chief of general staff's office.
He added that the drills would be based on the estimated military capabilities of Taiwan and China in 2006.
"We predict the war of the future will be non-lineal, no-contact and asymmetric in form. It's very likely that China will invade Taiwan with a surprise attack," he told reporters.
The manoeuvres are also expected to include a computer-simulated war, live-fire drills and missile testings.
Li added that various kinds of new weaponry would be tested, without elaborating.
Beijing has considered Taiwan part of its territory to be reunified, by force if necessary, since the two sides split in 1949 at the end of a civil war.
Cross-strait tension has been escalating since pro-independence Taiwan President Chen Shui-bian took office in 2000, despite booming trade and expanding civil contacts.
Taiwan and the United States say China is targeting the island with some 500 ballistic missiles. The mainland has repeatedly threatened to invade if it tries to declare independence.
Taiwan's defense ministry has warned of the possibility of an attack by China after 2008 unless the island continues to strengthen its defensive power as a deterrent.