The present study investigates the interpretation of embedded null arguments in L2 Chinese grammars of English-speaking learners. The article proposes that there are two types of null elements in Chinese: the syntactic deletion type (a purely syntactic category) and the discourse deletion type (a syntax-discourse interface category). The two types of null elements contribute to different interpretations of an embedded null argument. Therefore, the acquisition of the interpretation of embedded null arguments is intrinsically that of the two types of null elements in the embedded argument position. The recent Interface Hypothesis (Sorace 2005, Sorace and Filiace 2006) proposes that L2 learners do not have problems acquiring purely syntactic categories, whereas they do face difficulties acquiring categories relating to the syntax-discourse interface and may never succeed in this task. The results of a picture judgement task are not fully consistent with the Interface Hypothesis. L2 learners acquire both the syntactic deletion type of embedded null argument and the discourse deletion type. In particular, the discourse deletion type of embedded null object is acquired as early as the low-intermediate stage.