Abstract: A mathematical modeling is applied to illuminate and predict the mechanism of electron transfer in algae photosynthesis. A magnetic field can accelerate its reaction by decreasing the frequency of reverse reactions in the radical pair mechanism. The effect of magnetic field (MF) changes the rotational dynamic of the radical pair and in general alters the yield and lifetimes of its product. The external magnetic field applied to the system causes a radical pair reaction change. This phenomenon can be explained by a rate constant K3 for dual-reaction coordinate movement or triplet state formulation and according to the effect of the function rate dependent on magnetic K_ISC.