Abstract: Based on the comparison with observation and reanalysis data, the study evaluated the performance of the Atmospheric Model Intercomparison Project (AMIP) and the Coupled Model Intercomparison Project historical experiments (Historical) of the IAP/LASG climate system model FGOALS-g3 in simulating climatology and interannual variability of July–August–September seasonal-mean North Africa summer monsoon (NASM) and Sahel precipitation, explained the bias by moisture budget and regression analysis, and investigated the influence of ocean-atmosphere coupling by comparing AMIP and Historical. The results showed that both Historical and AMIP experiments underestimated precipitation, with weaker southwest monsoon winds and further southern rainfall positions. The pattern correlation coefficients of precipitation in the Sahel and North Africa monsoon regions simulated by AMIP are 0.80 and 0.62, respectively, which are 0.74 and 0.46 simulated by Historical, and the corresponding root mean square errors are 2.58 and 3.23 mm, which are 3.30 and 4.01 mm in the Historical experiment, indicating that the deviation of AMIP is smaller than that of Historical. Historical and AMIP both underestimated water vapor convergence over the NASM region, estimating less vertical moisture advection and evaporation and more horizontal moisture advection than observed, resulting in dry biases. In terms of interannual variability, the observation shows that summer monsoon rainfall in North Africa is negatively correlated with ENSO. AMIP can reproduce the ENSO–NASM negative relationship better than observation. However, Historical cannot reasonably simulate the relationship on the interannual time scale. AMIP overestimates ENSO circulation responses, including descending anomalies, weaker tropical easterly jets, and decreased low-level monsoons over North Africa, all of which contribute to the stronger precipitation negative anomaly. In contrast, Historical underestimates the above ENSO-related response, resulting in feeble precipitation negative anomaly. Vertical moisture advection anomalies, particularly the dynamic element of vertical moisture advection anomalies, dominate the ENSO–NASM negative relationship, according to moisture budget research. AMIP agrees with observation, but it overestimates the above term, resulting in more negative rainfall anomalies, while Historical overestimates horizontal advection and vertical thermodynamic anomalies, which indicates that horizontal advection anomalies cause the inhibited simulation of the ENSO–NASM negative relationship.