Abstract: Loosely type maize “Changyu 13”, semi-compact maize “Dongdan 60” and compact maize “Zhengdan 958” were planted in three planting densities (2 600 plant·667 m^-2, 3 200 plant·667 m^-2, 3 800 plant·667 m^-2) to explore effects of planting density on sucrose metabolism and activities of enzymes related to starch synthesis in different plant types of maize hybrids. The results show significant effects of planting density on sucrose content and activities of sucrose phosphate synthase and sucrose synthase in functional leaves with most beneficial effect of low planting density. Planting density presents less influence on activities of ADP glucose pyrophosphorylase and UDP glucose pyrophosphorylase in maize grains. It is illustrated that loosly type maize “Changyu 13” and compact maize “Zhengdan 958” are source-limiting hybrids, semi-compact maize “Dongdan 60” is pool-limiting hybrid. Effects of planting density on different types of maize are different. They are strongest on loosely type maize “Changyu 13”, weakest on impact maize “Zhengdan 958”.