This study is an qualitative case study which tried to find out the relations between reading abilities and sociocultural background knowledge regarding students of multicultural family. We had an interview with 8 students from multicultural family and their parents. Most of the parents had difficulties in communicating in Korean, so they had a great limitation to take care of their children's studying. The students had some difficulties in reading comprehension due to the lack of sociocultural background knowledge, in particular Korean vocabulary, proper words, homonym and idioms. The students generally accomplished to wite a summary in the form of "Topic and Comments", but sometimes they had mistakes such as omitting main points or adding unnecessary detail informations. We observed some student's lack of sociocultural background knowledge during their reading texts, we named it as "Humpty-Dumpty Gap" in this paper. The gap is an obvious obstacle in reading comprehension. So when teachers try to teach reading for the student, they need a careful intention regarding sociocultural background knowledge.