The large group of left-behind children with the absence of parental accompanying are likely to have serious physical and psychological problems, which may lead to serious public safety and social economic troubles in adulthood. Such unique phenomenon calls us attention on the impact of parents on household educational investment. Based on the data of China Family Panel Studies in 2014, This paper examines the effects of parents’ cognitive ability on household educational investment for their children. The research propositions were tested using multiple regression analysis methods. Results indicate that parents’ cognitive ability can significantly improve the level of monetary and non-monetary investment in education. We also find that compared with their counterparts, the cognitive ability of left-behind children’s parents fails to affect their household educational investment, due to the “parent-child separation effect”. Further analysis shows that improving the regional informatization level of parents of left-behind children can alleviate the “parent-child separation effect”, and finally facilitate cognitive ability’s role in increasing household educational investment. These findings enlighten education policy makers and households a feasible way to alleviate the imbalance and insufficiency of household educational investment among left-behind children families.