Second Language Acquisition (SLA) has benefited quite a lot from Construction Grammar. Most of the previous SLA researches adopting a constructionist approach have been primarily engaged in issues pertinent to the relevance of construction in SLA, the process of second language (L2) construction learning, and factors affecting L2 construction learning. This paper distinguishes itself from previous research by embarking on a new direction in the constructionist approach to SLA from the perspective of the constructional network. Specifically, it deals with how constructional network works in SLA and argues that L2 constructional network bears the imprint of and is reconstructed from L2 learners' L1 constructional network. The constructional network works in SLA in at least two ways which are manifested in the motivating function of vertical links in L2 learners' acquisition of schematic and complex constructions and the facilitative or inhibitive effect of horizontal links in L2 construction learning. Admittedly, our description of how the constructional network works in SLA is precursory and nonexclusive, and some general and specific issues are raised for future research.