Calculation of relation between the negative absorption coefficient a and the direction of the singular axes P.Q.has been made quantitatively for lasing condi- tions in Nd:YAP crystal for the first time,and this calculation is based on the complex Fresnel’s equation of the wave normals of light propagation in anisotropic medium.It is discussed by using this nature of singular axes that a circularly polarized laser beam output can be obtained.