Abstract: The simultaneous multi-species Planar Laser Induced Fluorescence technique plays an important role in studying the flame structure and the two-dimensional distribution of intermediate species in combustion.The experimental system of OH/CH₂O/Acetone-PLIF was built in order to study the CH₄-Air inverse diffusion jet (IDJ) flame.The system consists of two sets of lasers, two intensifier-CCD cameras, a temporal controller and several lenses.The strategy of fluorescence excitation, the method of synchronous timing control and image calibration procedures are discussed.The IDJ flame was studied using the simultaneous multi-species PLIF technique, and the reaction zone, pre-heating zone and fuel zone of IDJ flame were determined.Experimental results suggest that the IDJ flame is different from either the normal diffusion flame or the premixed jet flame.The behavior of this type of flame reveals similarity to the partially premixed flame.Compared to OH chemilumiscence images, simultaneous multi-species PLIF can provide more detail and information about the flame structure and it has huge potential in fundamental combustion studies and industrial burner experiments.