The spin coherence time of NV-with high concentration at room temperature is limited by the paramagnetic impurity and its spin, which is not conducive to the magnetic sensing with high sensitivity. To increase the coherence time, the dynamic decoupling (DD) process for NV- color center ensemble is studied in this paper. When the external magnetic field is fixed at 40 G,the resonant microwave frequency of |ms=0>→|ms=±1> is determined via continuous-wave optical magnetic resonance (CW-ODMR) spectroscopy. The Rabi oscillations between the |ms=0>→|ms=+1> with different microwave power have been observed and the optimal π-pulse length can be determined. Based on the typical CPMG-n sequence, the DD process with different number of optimal π-pulse is also studied. At a maximum input power of 130 mW, the optimal π-pulse length is 288 ns. Combined with CPMG-32 sequence, the coherence time is increased from 372(3) ns to 87(1) μs. These results show that we already have the basic technology of improving the coherence time with manipulation of quantum state, which is the foundation for the quantum magnetic detection with high sensitivity.