"The Chinese communists are likely to conduct small-scale or partial attacks in 2006 or 2008," Tsai said in parliament.
Asked why he thought the Chinese military would attack during that period, Tsai said because by "that time they may have acquired air and naval superiority (over Taiwan)" following Beijing's persistent arms build-up.
He urged approval of the 610 billion Taiwan dollars (18.2 billion US) special outlay for Taiwan's purchase of eight submarines, a modified version of the Patriot anti-missile systems PAC-III and a fleet of anti-submarine aircraft over a 15-year period commencing in 2005.
Taiwan government spokesman Chen Chi-mai said Tuesday that China's military spending had risen at a double-digit rate each year, amounting to between 50 billion US dollars and 70 billion US dollars last year.
China has repeatedly threatened to invade Taiwan should the island declare formal independence.
Taiwan's President Chen Shui-bian of the pro-independence Democratic Progressive Party (DPP) has pledged to amend the constitution before retiring in 2008 to reflect his group's separatist stance.
The DPP government insists the current constitution, enacted by the former Kuomintang (KMT) government, must be dramatically changed to meet Taiwan's needs, but Beijing sees the attempt as a step towards formal independence.
The US Defense Department warned in a report last month that China was developing "credible military options" to prevent Taiwan from achieving independence, including tools to discourage the United States from coming to the island's aid in a conflict with the mainland.
Separately, the defense ministry issued a statement denying a US report suggesting Taiwan could repel a Chinese attack by bombing China's Three Gorges Dam.
In its 2004 report to Congress on China, the US Defense Department said: "Since Taipei cannot match Beijing's ability to field offensive systems, proponents of strikes against the mainland apparently hope that merely presenting credible threats to China's urban population or high-value targets, such as the Three Gorges Dam, will deter Chinese military coercion."