Semantic comprehension of compound nouns is one of the subjects discussed in theoretical framework of cognitive linguistics. Compound nouns are divided into four groups based on the semantic relation of its components. According to the criterion of existence or absence of a semantic head, two main groups of endocentric and exocentric compound nouns are investigated in this study. A list of these nouns was collected as a library research from different texts and used to test this research. After examining multiple language comprehension tests, definition-word pairing test was used and in the form of an application on smart phones on Persian-learners of the middle level in Teaching Persian as a Second Language (TPSL) of Ferdowsi University of Mashhad was performed. Totally, 888 data were obtained from the test (37 subjects paired 24 definitions with compound nouns) described and analyzed by standard statistical tests. Finally, T and Pearson tests showed that due to the semantic head in endocentric compound nouns, the level of semantic comprehension of Persian-learners of endocentric compound nouns is greater than that of exocentric compounds. Besides, comprehension of Persian learners from Persian endocentric compounds is faster than exocentric compounds. Also, there is a correlation between the comprehension of Persian learners of endocentric and exocentric compound nouns. Therefore, the existence of a kind of relationship in endocentric compound nouns is understood more quickly than exocentric compound nouns. Therefore, the theory of Competition among Relations in Nominals (CARIN) is confirmed.