Electrical explosion of the thin golden wire is fundamental for the EBW detonator. In this paper, the expansion process of plasma generated in 0.04 mm wire explosion was captured using interferometry diagnostic. Moreover, the transient current during the electrical explosion was also measured in order to establish the connection between current and plasma expansion in time domain using a photoelectric transducer. 3D dynamic simulation of plasma expansion was conducted, in which JWL equation of state containing energy term was selected to describe the dynamic behavior of plasma. The results shows the simulation result was in good agreement with experimental results. And under the condition of 0.22 μF capacitor and 3900 V charging voltage, the expansion velocity of plasma reaches 8913 m·s^-1,and then 3000-4000 m·s^-1 after travelling for 1.63 mm. The pressure of plasma is higher than 2.4 GPa. The satisfactory agreement between simulation and experiment indicates that the JWL equation of state is suitable for plasma generated in electrical explosion. The simulation results show that the change of the pressure and density of plasma with travelling distance could be described using polynomial function. The result in this paper was able to give more insight of the mechanism of EBW detonator and thus provide suggestions for the design of the EBW detonator.