The new entry system has been announced in an attempt to reduce staff workloads as the popularity of the service grows and there is an increasing demand for tickets.
A maximum capacity is put on the audience for the event for safety reasons and a free ticket entry system was introduced to control the number of people entering the cathedral.
But a statement released by the cathedral this morning said the "increasing demand for tickets has added to the workload of staff, at an already busy time of year".
It continued: "The chapter of Truro Cathedral has therefore decided to streamline the entry system away from ticketing and introduce a system of queuing and hand-clicking people as they enter the cathedral.
"Once capacity is reached then of course no further entry will be allowed."
Canon Perran Gay, canon precentor and head of worship, said: "We hope that people will understand the reasons for this change and spread the word about it as widely as possible.
"In the last few years we have had to tell people as early as mid-November that there would be 'no room for them at the inn' at these services because all the tickets had already gone.
"Now it will be possible for people to decide even on the day itself that it would be good to go to church at Christmas, and (provided they are there in good time) there will be a place for them at these special services.
"And if we do reach capacity, then there are several other services where there will still be room, including Midnight Mass at 11.30 pm on Christmas Eve and our sung service on Christmas Day at 10am.
"These are also wonderful ways to celebrate Christmas together."
The service, designed by the first Bishop of Truro Edward White Benson, started at the cathedral in 1880 and has run unbroken for 132 years since.
The Festival of Nine Lessons and Carols will take place on December 23 and 24 at 7pm, with doors opening at 6pm.