There are elements of fact in it. Of course, there really were attempts to kill Hitler and other high ranking members of the Third Reich, and other films have been made about these. But the main idea of Tarantino's film - the idea of a special mission staffed by Jewish-American soldiers, to go behind enemy lines - also has some basis in fact.
It is now known that there was a Commando troop in Britain, consisting largely of Jewish soldiers, who did undertake a highly dangerous mission in World War II. Most of these men were refugees from Nazi persecution who were eager to join the fight against Hitler - another similarity with the film. However, Tarantino shows the men as baying for blood, whereas in real life they were sent to gather information and killed only when they had to.
You can read an interview with the son of one of these real-life heroes here.