This study investigated Chinese bilingual learners' subject knowledge co-construction and business English language use in a Technology-enhanced Content and Language Integrated Learning (TECLIL) programe. Four intact classes of Year One University business-major students were exposed to two different learning environments -- a TECLIL project-based learning environment using Knowledge Forum (KF), and a CLIL project-based learning environment. Data included student oral business presentations, written business reports, subject knowledge test results, student KF server log information, and online interaction records. The results indicated that the TECLIL project-based learning classes outperformed the comparison classes on both subject concept learning and business English language use. The quantitative analysis found that students' KF participation was associated with their content understanding and language development. Micro-level discourse analysis of students' online discussion notes further revealed bilingual students' productive discourse patterns in the TECLIL environment. Theoretical and pedagogical implications are discussed.