Based on the bench-scale impinging entrained-flow gasifier with coal water slurry (CWS) as the feedstock, the in situ breakup modes of the CWS at operating conditions were investigated using advanced visualization techniques. A new imaging approach was applied to obtain time-resolved images. The breakup modes were classified based on the atomization characteristics. The occurrence percentages of different modes were analyzed by statistical method. The results show that the primary breakup mode in the gasifier is the atomization mode. The secondary breakup modes in the gasifier, which depends on the velocity field and the entrainment of gas flow, are divided into the following groups: no breakup, tensile breakup, shear breakup and synergistic breakup. Synergistic breakup is a special breakup mode caused by the interaction of the opposed multi-burner, which improves the overall atomization efficiency in the impinging entrained-flow gasifier. Statistical analysis shows that the percentages of tensile breakup and shear breakup in the high velocity region are approximately equal and the main secondary breakup mode of the low velocity region is tensile breakup.