Radiative transport equation is used widely to model propagation of particles through a scattering medium, such as photon transport in tissues in optical imaging. In this talk, I will present instability analysis of an inverse problem of radiative transport equation with angularly independent source and angularly averaged measurement near the diffusion limit when the normalized mean free path is small. For the reconstruction of absorption coefficient, we show that the instability transition depends on the relative sizes between the mean free path and the perturbation in measurements.