Outlining his draft environment strategy last week, Khan said he wanted to encourage the development of more green roofs and walls which use grasses and plants to soak up rain water and pollution.
London’s boroughs are also to be able to access funds to invest in parks and improve community spaces and encouraged to improve air quality.
And local groups will be able to apply for the first £1m of the Greener City Fund to pay for neighbourhood tree-planting schemes and to maintain green community areas.
In order to achieve National Park City status, the mayor is working with partners across the capital to develop and define criteria.
These are likely to include: protecting existing green space; increasing access to green space, particularly in areas where these is little access; and improving the quality of green space.
Daniel Raven Ellison, National Park City campaigner, said: “Making London a National Park City is an opportunity to improve the health of all Londoners.
“One of our main goals is to make the majority of London physically green and we very much look forward to working with the mayor on this target.”
Julian Bell, chair of London Councils’ transport and environment committee, said, welcomed the mayor’s ambition.
“I look forward to reviewing the full strategy to ensure the role of the borough in improving London’s environment is reflected throughout,” he said.
“I am particularly pleased with the strategy’s approach to improving London’s green infrastructure.
"A greener London will not only be more pleasant to live in but will address the hug air quality problem London faces, support healthier lifestyles and help the city adapt to climate change.”
Other elements of the environment strategy includes a £10m energy efficiency delivery programme to help people power their homes affordably and policies to cut waste including setting minimum recycling standards.