The vessel is part of a submarine programme launched in 2016 that aims to deliver a fleet of eight vessels, but opposition lawmakers have criticised the repeated delays in the project.
Taiwan is seeking to upgrade its defences to deter China, which claims the democratic island is part of its territory and has threatened to use force to annex it.
Sea trials of the submarine began in June, nearly two years after it was first unveiled.
The original target was to wrap up testing by September 30 and deliver the submarine by the end of November, the navy said previously.
But Defence Minister Wellington Koo said Monday that sea trials were ongoing.
"All the sea trials were supposed to be completed by the end of November, but in fact that is no longer achievable," Koo told lawmakers.
"I want to emphasise again that everything we do is based on safety assessments and there's no rush to meet any specific month."
A spokesperson for CSBC confirmed the delay.
The submarine programme has been plagued by obstacles.
Koo admitted in October that the original timeline for construction had been unrealistic.
"In practice, we face many difficulties, especially given our own circumstances, including equipment issues and delays in scheduling the manufacturers' technical personnel," Koo said.
The submarine measures 80 metres (262 feet) in length, has a displacement weight of about 2,500 to 3,000 tons, and boasts combat systems and torpedoes sourced from the US defence company Lockheed Martin.
The main opposition Kuomintang party and the Taiwan People's Party, which together control the parliament, froze part of the programme's budget earlier this year.
The parties said they wanted to see the results of the submarine's sea trials before releasing the funds.
Taiwan's navy currently has two working submarines, Swordfish-class vessels bought from the Netherlands in the 1980s.
Over the same period, China has built itself one of the world's largest navies, with nuclear-powered submarines and aircraft carriers.
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