Speaking in China, the PM denied she had "gone soft" on migration and said people backed Brexit because they wanted "an element of control", the BBC wrote.
A points-based model would not let the government control arrivals, she said.
Ex-UKIP leader Nigel Farage said many people had voted Leave for the policy, backed by Boris Johnson among others.
Mrs. May is attending the G20 summit of world leaders in Hangzhou, her first international summit as prime minister.
Read alsoMerkel admits mistakes made in Germany, EU with refugee crisisAlthough Mrs. May supported remaining in the EU, she has said that the Brexit vote must be respected and suggested that curbs on the current free movement of EU citizens into the UK would be a red line in future negotiations with the EU.
But speaking to journalists in China she dismissed Vote Leave's proposal of an Australian-style points system for deciding the number of skilled and unskilled workers who could come into the UK every year from the EU and beyond – with numbers to be determined by MPs.
Rather than giving the government control, such a system would allow anybody into the UK if they met the criteria, she said, adding that curbs on student visas had been a more effective measure to reduce immigration.
"I want a system where the government is able to decide who comes into the country – I think that's what the British people want. A points-based system means that people come in automatically if they just meet the criteria," she added.
