The major goal of this research is to investigate learners' metaphorical comprehension in L1 and its effect on the metaphorical comprehension in L2 by Iraqi EFL learners at secondary school. In which, they encounter difficulties understanding English texts and lectures, primarily when metaphor is included, which leads to the misunderstanding of some or even the whole material. To this end, the research will utilize the 'Conceptual Metaphor Theory' by George Lakoff and Mark Turner (1980), and Cummins' Linguistic Interdependence Hypothesis (1979). The type of the survey of the data collection is a self-administered questionnaire. The questionnaire is classified into two divisions: the demographic part that gives a general background of the participants, and the part that includes 30 Arabic metaphoric proverbs and other 30 English proverbs. Each proverb is followed by four distractors from which a participant is required to choose the correct meaning for a certain proverb. The questionnaire was administered to 252 Iraqi convenience sampling. The findings showed that the participants who are more skilled in Arabic metaphor performed better in English metaphor. In addition to the significance of this study to the literature where, up to the researcher knowledge, no study has tackled the effect of the L1 on L2 in the Iraqi context, it presents a pedagogical contribution. In which, the study will draw the attention of the syllabus designers to the significance of developing cognitive skills of learners in L1 to achieve a better cognitive skills in L2.