Continuous wave optically detected magnetic resonance (CW-ODMR) is a practical way to study the sensitivity of the DC magnetic field. However, in large ensemble nitrogen-vacancy (NV) defects, the simultaneous excitation of microwave and laser will deteriorate the parameters of the ODMR spectrum and some unwanted sideband excitations caused by P1 electron spins will also bring challenges to further improve the sensitivity and signal quality. Here, we first achieve the CW-ODMR and acquire DC photon-shot-noise-limited magnetic sensitivity of 12nT/Hz. Different from the conventional method, we take advantage of pulsed quantum filtering (PQF) technology to eliminate such impacts above and demonstrate a sensitivity of about 1nT/Hz, which an order of magnitude enhancement over CW-ODMR. We find this method provides simple but effective support for relevant high-sensitivity DC magnetometry and obtains pure resonance signal when using large ensemble NV- defects.