The latest version of the capital’s key strategic planning document is due to be published for consultation on Wednesday.
A statement from the London mayor’s office, issued ahead of publication, says that the draft document "strengthens safeguards which prevent harmful development on vital green land both within and surrounding the capital".
The statement says that this "means a planning application which involves building on the green belt will be refused by the mayor if it does not meet strict rules on what is appropriate, such as replacing existing buildings with new ones of a similar scale or the provision of new agricultural buildings".
The statement says that the mayor will "work with London’s boroughs and other partners to ensure that public access to the green belt is maintained and that its overall quality is enhanced".
It also says that the draft London Plan will "strengthen protections" for metropolitan open land and "encourages boroughs to protect existing allotments and provide space for community gardening, including growing food, in new developments".
Khan said: "I firmly believe we can build the homes Londoners need without sacrificing the green belt. This will mean more development on brownfield land, town centres becoming denser, incorporating more green infrastructure in our streets and developments and being more creative with how we develop the hundreds of small sites across the capital."
Elsewhere, the statement says that the draft London Plan also includes "guidelines for increasing green infrastructure (such as street trees, green roofs, green walls and rain gardens) and a framework to help boroughs and developers determine how much should be required in new developments".
It says that the guidelines "make it clear that green infrastructure must form an integral part of new developments, rather than an ‘add-on’, and will be judged against a number of criteria, including promoting wellbeing, enhancing biodiversity and improving air and water quality".
City Hall has also announced that the new London Plan will contain "detailed policy guidance on the mayor’s manifesto commitment to put restrictions in place around new fast food outlets".
The document says that measures in the document will say that "new takeaways should not be permitted within 400 metres walking distance of an existing or proposed primary or secondary school". Where new takeaways are granted planning permission, they will be required to sign up to an initiative aimed to ensure the food produced is healthy.
The new London Plan will also "push local authorities to recognise the heritage, economic, social and cultural value of pubs and ensure they are protected for local communities", City Hall says.
A separate statement from City Hall says that the draft London Plan will include a policy to "make clear that any application for the exploration, appraisal or production of shale gas via hydraulic fracturing in London should be refused by boroughs".
The statement says that there have been "reports this year of energy companies identifying potential fracking sites in London".
But it adds that the mayor has "made his opposition to fracking clear in his mayoral election manifesto and his commitment is in line with the draft London Plan’s policies on boosting energy efficiency and renewable energy and preventing climate change, tackling London’s lethal air pollution, and protecting water resources".
The draft London Plan will be published on Wednesday and the public consultation will run until 1 March 2018.