Bainite microstructure is of considerable importance in the design of high strength steels because of its excellent balance of strength and toughness. The present work aims to deeper understand the complex bainitic phase transformation characteristics and to further develop a multi-phase field model which not only considers the bainitic ferrite formation but also takes the nano-sized carbide precipitation features into account. The spheroidized carbide dissolution and the bainitic microstructure formation in high carbon bearing steel 100Cr6 were characterized with respect to their morphology, phase fraction, crystallography and carbide size distribution by means of Light Optical Microscopy (LOM), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and X-Ray Diffraction (XRD). Atom Probe Tomography (APT) analysis was carried out to investigate the elemental partitioning behaviors during the spheroidized carbide dissolution and the bainite transformations. In order to analyze the nano-sized carbide precipitation type and phase fractions within the bainitic microstructures, Anomalous Small-Angle X-ray Scattering (ASAXS) was applied. In combination with the experimental characterization methods, the thermodynamics and kinetics calculations were performed using Calphad method and multi-phase field approach. Nano-sized cementite theta precipitation within the bainitic microstructure was taken into account in the simulation. The simulated phase transformation kinetics and microstructure evolution by multi-phase field modeling is validated by dilatometry, SEM and TEM. A state-of-art simulation approach for bainite transformation is proposed and further discussed.