Trump's numbers are — like several other of his statements throughout the rest of the campaign — untrue, in this case the result of some faulty math.
Facing criticism for not doing enough to help Syrians, U.S. Secretary of State John Kerry announced in September that over the next next fiscal year the U.S. would take in an additional 10,000 refugees from Syria. That comes along with a pledge to increase the total cap for refugees from 100,000 per year by 2017, with similar numbers of Syrians coming in up until that point.
(As a comparison, Germany has taken in about 57,000 refugees, mostly Syrians, this year.)
Trump's number seems to come from thinking all 200,000 refugees making it to the U.S. in 2016 and 2017 will be Syrians, instead of 30,000 tops. But it seems like 200,000 is becoming a meme. Sen. Rand Paul is also picking up on the larger number now, making the argument that 30,000 becomes 200,000 when those who arrive invite their families.