Precipitation of intragranular acicular ferrite (IAF) and interlocking microstructure is the chief principal, which can increase the strength and toughness of steel. Herein, the three-dimensional morphology and growth behavior of IAF is discussed. Focused Ion Beam, confocal laser scanning microscopy and electron backscattered diffraction were used. Results show that IAF was plate-like shape with much pits and defects, and needle-like with smooth surface which isolate in 750oC and 700oC for 1min respectively. The growth behavior of IAF and interlocking microstructure were studied. Additionally, we provide a theoretical basis for the three-dimensional morphology forming mechanism in a new perspective of IAF.