A major new national park will protect threatened species and provide green space for a growing city population.

Gulguer National Park, about 50km west of Sydney, will protect dozens of native threatened species and preserve Aboriginal rock art, artefacts and shelters.

The sprawling 1100-hectare space – set to be more than three times the size of Sydney's Centennial Parklands – will add about 700 hectares of new land acquired from old farming and rural residential development.

NSW Environment Minister Penny Sharpe said the park would protect at least 28 threatened species, including the powerful owl, southern greater glider, eastern coastal free-tailed bat and giant burrowing frog.

It will also provide stronger protection for critically endangered forest.

"There's also some more quirky animals like some large land snails that really occur nowhere else on Earth except through these areas," Ms Sharpe told reporters on Sunday.

The park forms part of a broader Cumberland Plain conservation plan to offset the impact of urban development.

About 73,000 new homes are expected to be built in western Sydney in the next three decades.

The conservation plan includes the separate, recently created Georges River Koala National Park.

Gulguer National Park would provide much-needed green space for the region, including campgrounds, walking and cycling tracks, Ms Sharpe said.

"It's why these spaces are so precious and so important into the future," she said.

"It's making sure that people have access to nature and that we can also build the houses that they need."

Deputy Premier Prue Car said the park would give families access to outdoor spaces other parts of Sydney took for granted.

"At a time when families are under pressure, this new national park will give locals a world-class destination right in their own backyard," she said.