The base will be home to HMS Queen Elizabeth and HMS Prince of Wales, the largest ships ever built for the navy.
Work on Portsmouth's jetty, built in the 1920s and last upgraded in the 1970s, has begun, with upgrades expected to be completed next autumn.
It forms part of a Â£100m infrastructure package to prepare the base for the arrival of the first carrier.
HMS Queen Elizabeth measures 280m (300 yards) long and can travel up to 500 miles (800km) a day.
The ship's systems are being tested and it will conduct sea trials next year before being handed over to the Royal Navy.
It is expected to come into service in 2020.
HMS Prince of Wales is being constructed at shipyards around the UK before it is assembled at Rosyth.
Once completed, the revamped naval base is expected to create hundreds of jobs in Portsmouth.
In November 2013, BAE Systems announced it was ending shipbuilding in Portsmouth, leading to 585 voluntary redundancies, 160 compulsory redundancies, and the redeployment of 175 members of staff.
The Royal Navy has released an image of planned improvements to a jetty at Portsmouth Naval Base.