Based on connectivism and writing as process approach, this paper aims to construct a teaching model within the blended learning mode. Then, this teaching model will be practiced in English writing class for 16 weeks. According to writing exam, 64 students are selected to be our participants in the research. 32 students are classified in the control group in which traditional teaching mode is employed in writing class. Other 32 students are defined as experiment group in which students are taught in the teaching model within the blended learning mode. The data from pre-test and post-test have been made in paired sample T tests. The results from online course platform and pre-test and post-test suggest that the teaching model within blended learning mode can significantly improve students’ English writing ability in terms of four aspects: content relevance, content sufficiency, organization structure and language expression.