Twin zone cooling process with high extraction ratio is established by studying the effect of cooling rate on the boron extraction ratio of boron-containing slag. The viscosity increases rapidly by continuous cooling and the prior crystallization of forsterite, which hinders the nucleation and growth of suanite, result in the low extraction ratio of boron. With the twin zone cooling process, the rapid cooling in 1500°C-1200°C, restrains the formation of forsterite and reduces the inhibition effect of forsterite on the nucleation and growth of suanite. Heat is preserved at 1200°C to ensure the sufficient interaction time among the particles, which is favorable toward the nucleation and growth of suanite. As a result, the extraction ratio of boron-rich slag is improved.