Work to the ground floor of B Block, which the entrance is within, is being undertaken to improve the building and add new services.
The B Block entrance will close from 16 September 2016 until May 2017.
The redevelopment work will give visitors a better experience when they arrive.
Oxleas NHS Foundation Trust took ownership of QMH in October 2013, after South London Healthcare Trust was dissolved, and agreed to invest £30m to redevelop the site and improve facilities.
This latest development will see an out-patients area introduced for adult learning disability patients, with pharmacy and blood testing services on the ground floor.
The Urgent Care Centre is also being improved, and will have its own entrance for the 24/7 service it offers.
The first floor will provide out-patients with a range of clinical specialities including orthopaedics, general medicine, cardiology, women’s services and therapy services.