The invention discloses an impedance matching unit, a system and a method used for calibrating a high-frequency current sensor. The impedance matching unit is a transmission line structure formed by a radio frequency coaxial line with the characteristic impedance being 50ohm. The high-frequency current sensor is installed at a central position inside the impedance matching unit. The transmission line structure comprises a radio frequency coaxial input end, a radio frequency coaxial output end and a shell, wherein a core wire inside the transmission line structure penetrates through the radio frequency coaxial input end and the radio frequency coaxial output end; and the shell transits towards the middle from the radio frequency coaxial input end and the radio frequency coaxial output end so as to form a conical transition structure. The impedance matching unit disclosed by the invention solves a technical problem in relevant technologies that broadband characteristics of the high-frequency current sensor cannot be authentically reflected due to a calibration result of a high-frequency current sensor performance detection method in a high frequency interval has great distortion because of deficient impedance matching and bandwidth and the like.