The invention provides a real-time while-drilling gamma forward modeling geo-steering drilling method which includes the steps of in the geo-steering drilling process, based on a pilot stratum model, carrying out real-time forward modeling on while-drilling gamma logging response according to an actually-drilled well track, and carrying out comparative analysis on actually-measured while-drilling gamma logging data to provide the basis for updating the stratum model and adjusting the well track. A while-drilling gamma logging real-time forward modeling computing method based on the stratum model is provided and includes the steps of decomposing the stratum model according to a contact relation between a gamma logging detecting range and a stratum interface, and based on the attenuation law of gamma rays in a stratum, respectively analyzing and computing gamma ray fluxes of areas after the model is decomposed at the positions of detectors. When the real-time while-drilling gamma forward modeling geo-steering drilling method is used for real-time geo-steering, rapid real-time forward modeling can be carried out on a while-drilling gamma logging curve, and therefore the basis is provided for updating the stratum model and adjusting the well track.