This study examined the direct and indirect effects of critical thinking skills (CTS) on L2 writing (L2W) by taking CTS as the most important independent variable and other linguistic variables as mediators. The theoretical model includes 1 structural and 5 measurement models, involving 5 latent and 13 observable variables. 232 third-year English majors from nine intact classes of four provincial universities in China participated in the study. Three major findings emerging from the quantitative analysis are as follows: CTS are found to exert total effects on L2W via linguistic variables; CTS show direct effects on L2W and CTS have indirect effects on L2W via linguistic variables. The findings broaden the visions of related fields and call for attentions to the contributions of CTS as well as linguistic factors to L2W.