By using time-resolved photoluminescence and time-resolved Kerr rotation, we have studied the unique electron spin dynamics in InAs monolayer (ML) and submonolayer (SML), which were sandwiched in GaAs matrix. Under non-resonant excitation, the spin relaxation lifetimes of 3.4ns and 0.48ns were observed for 1/3ML and 1ML InAs samples, respectively. More interestingly, the spin lifetime of the 1/3ML InAs decreased dramatically under resonant excitation, down to 70ps, while the spin lifetime of the 1ML sample did not vary much, changing only from 400 to 340ps. These interesting results come from the different electron-hole interactions caused by different spatial electron-hole correlation, and they provide a direct evidence of the dominant spin relaxation process, i.e. the BAP mechanism. Furthermore, these new results may provide a valuable enlightenment in controlling the spin relaxation and in seeking new material systems for spintronics application.