Activists shouted slogans against a crew from the network as they arrived to cover a meeting of Commonwealth countries in Colombo on Friday.
"Channel 4 divides Sri Lanka, supports terrorism," said a poster carried by a demonstrator at the Bandaranaike International Airport, where the authorities rarely allow any hostile receptions.
"Channel 4. You lie because you are paid by LTTE," said another, referring to the defeated Liberation Tigers of Tamil Eelam militant group.
The demonstrators said they were told the director of "No Fire Zone: Sri Lanka Killing Fields", Callum Macrae, was arriving Monday and they wanted to register their opposition.
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The documentary, which has been watched by world leaders, accuses the Sri Lankan military among other things of executing surrendering rebels, which Colombo denies.
Sri Lanka had previously blacklisted Channel 4 staff involved with the documentary, but allowed them access ahead of the 53-member Commonwealth Heads of Government Meeting (CHOGM