In a letter to the body he asked for advice on “opportunities to simplify” the charge and make it “fit for purpose”.
It will consider changing or scrapping some reliefs and exemptions, such as the one for people selling their house.
Capitals gains is charged at 28 per cent on the sale of second homes and buy-to-let properties.
Almost 300,000 people paid the levy in 2017-18, generating just under £60 billion for the Exchequer.
Chancellor Mr Sunak has cut taxes in some areas to stimulate growth, including a stamp duty holiday and slashing VAT for the hospitality sector.
But economists have warned they’ll have to rise in others given the sky-high spending to get the country through the coronavirus pandemic.
A Treasury source played down speculation of a hike in capital gains.
They said: “It’s standard practice to review taxes and it’s one of the taxes that hasn’t been reviewed yet.
“There’s no expectation anything substantive will come out of it.”