In this Letter, we propose a simple and robust method that we have named an optimal accumulation algorithm (OAA) to modulate a scattered light field. Compared with the simulated annealing algorithm (SAA) and genetic algorithm (GA), the OAA is very robust, that is to say it has a strong anti-disturbance capability. In experiments, the scattered light field through ground glass and a polystyrene suspension was modulated, where the polystyrene suspension supported a dynamic random disturbance. It was found that, even if the suspension is too thick to see the ballistic light, the OAA can still modulate the scattered field effectively, while the SAA and GA completely failed. In addition, the OAA is so simple that only addition and comparison are needed, and it can achieve multi-target modulation.