Abstract: To improve the effect of detecting base materials by using passive millimeter wave imaging system (PMMW), the man-made chemical coated carbon fiber were added in detected materials and the composites were tested. Test results show that, for silver-nickel-coating carbon fiber (ANCF), copper-nickel-coating carbon fiber (CNCF) and nickel coated carbon fiber (NCF), the detected comparative voltage is decreased successively, but then the imaging distinguishing effect is improved accordingly. For base materials detected by PMMW, the esters or flour has little effect on imaging, while the graphite has slight one. After adding NCF with 0.3% weight into the above three base materials, the images are improved greatly in PMMW.