We present the theoretical results of the electronic band structure of wurtzite GaN films under biaxial strains in the(1122)-plane．The calculations are performed by the κ·p perturbation theory approach through using the effectivemass Hamiltonian for an arbitrary direction.The results show that the transition energies decrease with the biaxial strains changing from-0.5% to 0.5%.For films of(11(2)2)-plane,the strains are expected to be anisotropic in the growth plane.Such anisotropic strains give rise to valence band mixing which results in dramatic change in optical polarisation property.The strain can also result in optical polarisation switching phenomena.Finally,we discuss the applications of these properties to the(1122)plane GaN-based light-emitting diode and lase diode.