Whether diagram helps text learning or not continues to be debated. Recent research evidence shows mixed results that diagram can either enhance or hinder text learning in recent years. Yet, no recent meta-analysis has addressed the question: can diagram help learning? If can, how much? The current study summarized the definition of diagram, and searched for related studies from 2005 to 2015. 11 studies with 809 participants were analyzed. A significant small to medium effect size was found between learning with text only and learning text with diagram. The overall effect size (95% CI) is 0.38 (0.12, 0.64) with marked heterogeneity (I² = 72%) using the random-effects model. Subgroup analysis results show that learning with arithmetic diagram hinders learning significantly, and participants performed better in transfer tests.