The theoretic expressions of loss in different scattering orders are analysed by imitating random migrations of photons in free space. The predicted path loss under different elevation angles are presented and compared with relevant literature to validate it. It can be concluded from the simulation that under specific preferences, high orders of scattering (higher than four orders) contribute little to the total energy of received optical signal (at least 10 orders of magnitude smaller), and thus the effects caused by the 4th or higher orders of scattering can be neglected.