The fine structure splitting (FSS) of exciton emissions from single InAs/GaAs quantum dots (QDs) are investigated. The excitonic FSS is attributed to the QD shape asymmetry reduction. Through the formulism of the Bir-Pikus Hamiltonian, the relationship between the FSS and strain is discussed. The excitonic FSS can be manipulated by applying in-plane magnetic field. We have discussed the reason that causes anti-crossing of the two bright exciton state. By applying external stress, the FSS and the eigenaxes of QDs can be changed simultaneously.In the experiment, the degree of anti-crossing do improved under external stress assistance.By combining these two methods, the single quantum dot excitonic state can be recovered to degeneracy