A systematic investigation about the strain distributions around the InAs/GaAs quantum dots using the finite element method is presented.A special attention is paid to influence of an Ino.2 Gao.sAs strain reducing layer.The numerical results show that the horizontal- and vertical-strain components and the biaxial strain are reinforced in the In As quantum dot due to the strain-reducing layer.However,the hydrostatic strain in the quantum dot is reduced.In the framework of eight-band k.p theory,we study the band edge modifications due to the presence of a strain reducing layer.The results demonstrate that the strain reducing layer yields the decreasing band gap,i.e.,the redshift phenomenon is observed in experiments.Our calculated results show that degree of the redshift will increase with the increasing thickness of the strain-reducing layer.The calculated results can explain the experimental results in the literature,and further confirm that the long wavelength emission used for optical fibre communication is realizable by adjusting the dependent parameters.However,based on the calculated electronic and heavy-hole wave function distributions,we find that the intensity of photoluminescence will exhibits some variations with the increasing thickness of the strain-reducing layer.