Abstract: Based on the theories of Ostwald ripening, the coarsening law of Ti(C, N) in 20CrMnTi gear steel was calculated at 930℃. The results show that when the holding time is 1, 2, 4, 8, 16 h, with the increase of holding time, the coarsening of Ti(C, N) particles would occur to some extent. While the coarsening rate coefficients m of second phase is greater, the coarsening is more serious. The range of d_t which is the average size of the second phase at t time is 2.64-16.2 nm and 3.33-20.4 nm when the holding time is 8 h and 16 h respectively with the maximum deviation 13 nm and 17 nm apart. So Ostwald ripening has little effect on the particle size of second phase Ti(C, N), and it is the original size of the particles that has the main influence on pinning the grain boundaries and preventing austenite grain growth.