Signal crosstalk can produce significant fringing effects on the observed images in a focal plane channel. Based on the earth and lunar observation data, the on-orbit detection of the crosstalk effects of all bands of the medium resolution spectral imager (MERSI-II) as FY-3D core load, and the preliminary correction tests also done. The detection results indicate that there are significant signal crosstalk phenomena of bands in some MERSI-II focal planes, among which the band 5 and band 6 of short-wave infrared focal plane and the bands 20, 21, 22, and 23 of mid and long wave infrared focal plane are suffered most obviously, manifested as inter-band and inter-detector characteristics, respectively. Based on the lunar point source imaging characteristics, the crosstalk coefficient is calculated using the linear approximation correction algorithm. Moreover, this correction algorithm is preliminarily verified through band 20. The results show that crosstalk correction can effectively remove the crosstalk signals of lunar images and significantly improve the fringe phenomena of earth observation images, implying that the proposed algorithm has good applicability.