Fluorescence　molecular　tomography　has　become　a　promising　technique　for　in　vivo　small　animal　imaging　and　has　many　potential　applications.　Due　to　the　ill-posed　and　the　ill-conditioned　nature　of　the　problem,　Tikhonov　regularization　is　generally　adopted　to　stabilize　the　solution.　However,　the　result　is　usually　over-smoothed.　In　this　letter,　the　third-order　simplified　spherical　harmonics　approximation　to　radiative　transfer　equation　is　utilized　to　model　the　photon　propagation　within　biological　tissues.　Considering　the　sparsity　of　the　fluorescent　sources,　we　replace　Tikhonov　method　with　an　iteratively　reweighted　scheme.　By　dynamically　updating　the　weight　matrix,　L1-norm　regularization　can　be　approximated,　which　can　promote　the　sparsity　of　the　solution.　Simulation　study　shows　that　this　method　can　preserve　the　sparsity　of　the　fluorescent　sources　within　heterogeneous　medium,　even　with　very　limited　measurement　data.