The charity condemned the prime minister, accusing him of failing to stop "UK tax havens facilitating tax evasion and other serious crimes".
Speaking in his Witney constituency Christian Aid's Campaigns Strategy Lead, Helen Collinson said: "We're here in the Prime Minister's constituency to remind him that people around the world are suffering because he has failed to stop UK tax havens facilitating tax evasion and other serious crimes.
"Mr Cameron promised to put the UK's own house in order in 2013 but, three years later, we are still waiting for UK tax havens to reveal who really owns the hundreds of thousands of companies they host, some of which are used in tax evasion and corruption.
"The leaked Panama Papers have revealed to everyone what powerful people and companies get up to when they can hide their tracks.
"David Cameron has just two weeks to clean up the UK-controlled tax havens before he hosts an international Anti-Corruption Summit in London. If he fails to take the necessary action it would leave a gaping hole in his credibility as a leader in the fight against corruption."
Christian Aid is calling on the PM to require UK tax havens to create public registers of the real owners of the companies they host.
Tax havens allow companies to hide who really owns and controls them, meaning they can avoid paying the full amount of tax.