This paper aims to examine the null-subject phenomenon in Mandarin Chinese, a discourse-oriented radical pro-drop language, and the factors that contribute to the presence/absence of overt subject pronouns in the language. A questionnaire survey was conducted among 11 Chinese high school students to collect data regarding the usage of null subjects by native Mandarin Chinese speakers. Three discourse factors that affect the distribution of null subjects, namely: 1) register, 2) speakers’ agency, and 3) nature of information conveyed by subject pronouns, are identified and analysed based on the collected data. Therefore, we should pay more attention to pragmatic factors when refining syntactic theories regarding null-subjecthood in future studies.