This study aims to investigate the acquisition of three Chinese modal auxiliary verbs: NENG, HUI, and KEYI by English-speaking learners who study Chinese as a foreign language and attempts to examine the following issues. 1) Are English-speaking learners able to distinguish the semantic difference between NENG, HUI and KEYI and realize their corresponding syntactic constraints? Does leaner’s acquisition of these three auxiliary verbs increase with the improvement of their Chinese proficiency level? Can these three auxiliary verbs be mastered completely by English-speaking leaners? 2) What is the acquisition order when they are learning NENG, HUI and KEYI? Furthermore, what is the acquisition order of the multiple semantic meanings within one single Chinese modal auxiliary verb? 3)What is the relationship between English-speaking learners’ comprehension and production, in regard to their performance on learning these three auxiliary verbs? 4) whatpedagogical implication does this study reveal? This research is composed of a comprehension test and production analysis. A questionnaire is designed to test English-speaking learners’ comprehension of NENG, HUI and KEYI, including fourteenmultiple choices questions. In addition, 275 essays from the participants are collected anonymously as production database to be analyzed. In total, 90 English-speaking learners who enrolled in Chinese courses at University of Massachusetts Amherst in Spring 2019 were participated, and they were divided into three experimental groups: beginning level, intermediate level, and advanced level. 60 native Chinese speakers were also invited into this research, served as a control group. The result in this research shows that 1) English-speaking leaners’ acquisition of NENG, HUI and KEYI do not always increase with the improvement of their Chinese proficiency level. Both HUI and KEYI present the same trend, which rises rapidly and significantly after experiencing a relatively flat stage, while the development of NENG is shown by U-shape learning curve. 2) For English-speaking learners, the acquisition order is(from the easiest to hardest): HUI > KEYI > NENG. 3) English-speaking learners’ production of NENG, HUI, and KEYI is not always parallel to their comprehension. Also, some implications for teaching NENG, HUI and KEYI are discussed in this thesis.