Bubble behaviors in non-Newtonian fluids are widely applied in many industrial processes such as enhanced oil recovery,wastewater treatment,polymerization and production of foods and pharmaceuticals,etc.[1] Coalescence and breakup between bubbles alter bubble size distribution and interface area,which has significant influence on gas-liquid mass transfer or chemical reactions [2].In this study,VOF method [3] was applied to study coalescence and breakup process of multiple bubbles rising in power-law non-Newtonian fluids.The effect of bubble number,initial bubble diameter,initial bubble interval and flow index of non-Newtonian fluids on bubble coalescence and breakup were investigated systematically.According to Suratman number and initial bubble interval,two different regimes of bubble coalescence and breakup were identified: all bubbles coalesce into one big bubble and part of multiple bubbles coalescence,the coalescent big bubble could breakup depending on hydrodynamics and physical properties of fluids.For two or three parallel bubbles,only the first regime takes place; coalescence and breakup process for four parallel bubbles was more complicated due to the intense interactions between bubbles,other than four bubbles coalescing into one big bubble and subsequent breakup,the middle two bubbles or two bubble pairs tend to collide and coalesce with each other.The study indicates that whether bubbles will coalesce depends mainly on initial bubble interval between bubbles,while coalescence and breakup process was affected by bubble size and rheological properties of non-Newtonian fluids via altering bubble shape and flow field structure.