The second-order cross correlation function of the photon emission and the polarization density matrix of the photon pairs emitted from the biexciton system of single semiconductor quantum dots under pulsed excitation were calculated using the dynamical population density matrix equations and quantum regression theorem. The entanglement of the photon pairs emitted from the single quantum dot with degenerate exciton states were investigated, and the relationship between the entanglement and the spin relaxation rate was also discussed. The simulations revealed that the spin relaxation destroys the entanglement of the photon pairs emitted from this system.