This study aims to clarify the cause of errors analyzing the Korean corpus of Chinese learners to represent the aspect of the errors both in the formations with the substitution errors in adnominal endings and in the structural patterns with adnominal clauses. As a result of analyzing substitution errors of adnominal ending forms according to the formation, this study shows that the learners have difficulty using ``-(았/었)던`` while they are familiar with using adnominal ending ``A-(으)ㄴ``. The most frequently substituted adnominal ending forms are ``V-(으)ㄴ`` and ``-는``. As a result of analyzing substitution errors according to the structural patterns, the learners are familiar with using adnominal ending forms in relative clauses and relative phrases, however, they have trouble in using adnominal ending forms in appositive clauses. There are three reasons Chinese learners have a problem with using adnominal ending forms: First, they lack understanding Korean grammatical characteristics of adnominal ending forms which are complicated in meaning and usage according to the forms related to the Korean grammatical categories of tense, aspect and mood are closely linked to one another, while there is only one relative marker ``的`` in Chinese without grammatical characteristics. Second, they are short of understanding relative tense which shows a difference in the tense of the main clause and the tense of the subordinate clause. Also, they lack understanding the grammatical restrictions on attaching adnominal ending forms to the nouns or bound nouns.