The development of e-learning and digital campus has prompted more and more teachers to assign online homework to students. Consequently, teachers need to provide sufficient and relevant guidance for such homework. Teachers' online homework guidance (TOHG) is conceptually connected with their level of technological pedagogical content knowledge about educational use of Web (TPACK-W). This study employed two questionnaires: a self-developed questionnaire for TOHG and a revised TPACK-W questionnaire to study how TOHG is associated with TPACK-W through correlation and regression analysis. Two hundred and eighty-four teacher participants from China who had experience in assigning online homework were asked to complete the questionnaires. This study validated the questionnaires and established significant relationship between the TOHG and TPACK-W. The study expanded current understanding of TPACK through the factors associated with online homework. The findings showed that the level of teachers' online homework guidance was significantly related to their TPACK-W, and the two factors of Web-Pedagogical Knowledge and Web-Pedagogical-Content Knowledge in the TPACK-W questionnaire could predict the TOHG. Future teachers' professional development for the construction of TPACK-W should include discussions and guidelines of online homework.