An absorber is a major component in absorption refrigeration systems, and its performance remarkably affects the overall system performance. A mathematical model for ammonia bubble absorption was developed to analyze the mechanism of the binary nanofluid enhancing bubble absorption. It considers the effects of nanoparticles on heat transfer, mass transfer, and bubble size in bubble absorption. It agrees well with experimental results in an ammonia-water mixture without nanoparticles, and the maximum relative error is less than 8.2%. The prediction shows that the most significant factor affecting the average absorption rate is the mass transfer enhancement caused by the nanoparticles addition. The average absorption rate increases nonlinearly with the effective mass diffusivity of the binary nanofluid increasing. This article presents a better understanding of the mechanism of the binary nanofluid enhancing bubble absorption in thermally driven absorption refrigeration systems.