Abstract: Three-phase three-limb transformers are widely used in power systems. An accurate model of three-phase three-limb transformers benefits the analysis of electromagnetic transients of the transformer and its protections. The classical BCTRAN model is widely used in the electromagnetic transient simulation of transformers. However, BCTRAN model can not accurately simulate the deep saturation phenomenon at each terminal. In this paper, a three-phase BCTRAN model is built to represent the coupling between the windings of three-phase three-limb transformers using sequence-component parameters. Deep saturation inductances are measured and determined using the hybrid source method to create the magnetizing branch, including the deep saturation region. Based on the classical BCTRAN model, an improved BCTRAN model for three-phase three-limb transformers is proposed considering deep saturation of iron core. Inrush current experiments on a 300VA three-phase three-limb transformer and a finite element model of 22kVA three-phase three-limb transformer show that the first peak error of inrush current of the improved BCTRAN model is smaller comparing with the traditional model. Experimental results show that the improved BCTRAN model of three-phase three-limb transformers can accurately represent the saturation characteristics and provide a basic transformer model for the study of electromagnetic transients of three-phase three-limb transformers.