Grammatical competence plays a very important role in second language acquisition and development. Therefore, with the help of the qualitative analysis software (Nvivo 11), this study employs a combination of content analysis and thematic analysis to synthesize researches related to L2 grammatical competence published between 1981 and 2020. Research findings show that the number of reseraches related to L2 grammatical competenc has been on the rise; the majority of the empirical studies are focused on university students; most of the research themes place great emphasis on interlanguage and L2 learners; with regard to the theoretical frameworks, most studies adopt the linguistic, cognitive and psychological frameworks. Besides, quantitative research and mixed methods research dominate the empirical research. Finally, the paper puts forward some suggestions for future research on L2 grammatical competence.