A linear transient nine-level primitive equation model has been developed to test three hypothesized mechanisms (residual, transient, and remote forcing) by which the blocking is initiated and maintained. Residual forcing consists of the time-average of the product of perturbations and diabatic heating anomaly. Transient forcing is represented by the time-average of the divergence of the vorticity flux with only synoptic-synoptic wave interactions. Remote forcing is derived from outgoing longwave radiation (OLR) using a vertical distribution of parameter;The model forcing is based on blocking anomalies, which is the difference between the blocking and nonblocking composites. The standing mode of the model is the nonblocking composite flow and the transient mode is the blocking anomaly flow;The results of model simulations show that both the Pacific and Atlantic control runs (including all three forcings) can simulate blocking in terms of spectral and energetics analyses, its time evolution and its spatial structure. By comparing different forcing experiments with the control run, we investigate the effect of the three forcings on the formation of blocking;The results of experiments show that residual forcing is the primary forcing for the formation and maintenance of both Pacific and Atlantic blocking, although the mechanisms which cause blocking in these two oceans are different. Pacific blocking is forced by the amplification of ultralong waves, either baroclinically or barotropically. Atlantic blocking occurs because of feedback effects between intense synoptic-scale waves and ultralong waves. The model simulations also suggest that if the statistical characteristics of forcing are correctly presented, the model will produce the correct climate;Time-mean transient forcing is a minor forcing in the formation and maintenance of both Pacific and Atlantic blocking. The intensity and location of blocking are only slightly affected;Experiments with tropical (remote) forcing indicate that this forcing does not directly intensify the blocking flow, but rather amplifies the divergence circulations (and enhances the splitting of strong westerly flow) to provide a favorable environment for the formation of blocking.