Abstract：Abstract:This study conducts a metaanalysis of the task complexity effects on L2 writing by synthesizing 41 empirical studies published at home and abroad from 2007 to 2017. The results show that: 1) the studies are mainly singlefactor ones which mostly take resourcedirecting dimensions of task complexity as the independent variables; 2) the language assessment measures are diversified, unbalanced in distribution and probably uncomparable; 3) resourcedirecting task complexity exerts significant positive effect on complexity and fluency, but shows nonsignificant positive effect on accuracy; 4) while producing significant negative effect on accuracy and nonsignificant negative effect on syntactic complexity, resourcedispersing task complexity has nonsignificant positive effect on fluency and lexical complexity; 5) cognitive load is the mediating variable affecting task complexity effect, and writers L2 proficiency, language assessment measures and task complexity dimensions are the moderator variables.
