The invention provides an ion current density measurement system. The system comprises an ion current sensing array, a data acquisition unit, an optical fiber data transmission unit, an optical fiberdata receiving unit and a battery power supply module. The ion current sensing array is used for measuring ion current density and converting into analog voltage signals to output. The data acquisition unit is used for converting the inputted analog voltage signals into first digital signals and sending to the optical fiber data transmission unit. The optical fiber data transmission unit is used for converting the received first digital signals into optical pulses and sending to the optical fiber data receiving unit through optical fibers. The optical fiber data receiving unit is used for converting the received optical pulses into second digital signals and sending the second digital signals to an upper computer. In the ion current density measurement system, by adoption of an optical fiber line for data transmission, great anti-jamming performance and large effective transmission distance of the transmission line are realized, the requirement of distant measurement can be met, errorsor faults in a data transmission process are reduced, the system is especially suitable for electric field measurement in a high-voltage environment, and high and low voltage isolation is realized.