The high-sensitivity magnetic sensor is the key to the weak magnetic and extremely weak magnetic detection imaging. In this paper, based on ensemble nitrogen-vacancy (NV) color center in diamond, a wide-field magnetic field distribution imaging system combined with the magnetic flux concentrator (MFC) is built for enhancing the magnetic detection. The paired T-shape chip MFC structures are designed and prepared based on the simulation of magnetic flux concentration effect, and the enhancement of magnetic field of MFC is verified by continuous wave optical detection magnetic resonance (CW-ODMR) imaging technology. When the gap width between the MFCs is 1.0 mm, the magnetic enhancement factor is about 10.35. To verify the effectiveness of the magnetic enhancement effect of the MFC, The magnetic enhancement effects are also measured under different magnetic field strengths and different gap widths. The magnetic sensitivity of the system increases from 1.10 nT/Hz^1/2 to 0.30 nT/Hz^1/2. By comparing the simulations with the measurements, the relationship between the measured magnetic enhancement multiple and the gap width can be obtained, and the better magnetic enhancement capability and sensitivity of the experimental system are also estimated. When the MFC’s gap width is 0.5 mm, the corresponding magnetic enhancement factor is increased to 18.21, and the corresponding magnetic sensitivity is 0.25 nT/Hz^1/2. These results show that the magnetic detection sensitivity of the ensemble NV in diamond can be effectively improved based on magnetic flux concentration effect, which provides a reference for the applications of precision quantum measurement technology in weak magnetic and extremely weak magnetic detection.