For the widely coverage of satellite beam, the dominated weather-caused attenuation on Ka-band causes the asymmetric fading of satellite uplink and downlink. The widely recognized adaptive coding and modulation (ACM), a significant fading mitigation technique in satellite communication systems, mainly focuses on improving the downlink spectrum efficiency. However, the uplink spectrum efficiency is always impaired when downlink channel condition is poor. In this paper, we propose a novel ACM scheme for geostationary (GEO) regenerative satellite systems, on which the on-board processing is based. To be more practical, two transfer modes: Transparent-transfer and Regenerative-transfer are designed. Nevertheless, regenerative transfer mode would result in data overflow on the satellite in the case of the selected uplink modulation and coding order is higher than the downlink. In this paper, a dynamic bandwidth allocation scheme is also designed to avoid that. At last, simulation results highlight the spectral efficiency improvement of the proposed on-board processing ACM scheme over the existing ACM scheme.