In order to mitigate the drying shrinkage of foamed concrete, lightweight aggregates (shale ceramsite and fly ash ceramsite) were used to prepare foamed concrete. Effects of lightweight aggregates on the compressive strength, drying shrinkage, internal humidity and pore structure of foamed concrete were studied, and the internal curing mechanism of lightweight aggregates was analyzed. Experimental results reveal that lightweight aggregates can adjust the internal humidity of foamed concrete, restrict the deformation of the matrix, and decrease the drying shrinkage of foamed concrete. However, lightweight aggregates can also introduce defects in foamed concrete, resulting in the decrease of compressive strength. The ink-bottle pores larger than 100 nm in lightweight aggregates are the control factor of efficient internal curing. The lightweight aggregates with more ink-bottle pores larger than 100 nm tend to possess stronger water release capacity and better effect of internal curing, thus resulting in lower drying shrinkage of foamed concrete.