A reference current source circuit includes a reference voltage generating module, a voltage buffer, an equivalent resistance, a filter capacitor, a current mirror module and a reference current outputting terminal. The voltage buffer includes an operational amplifier and a first FET. The current mirror module includes a second FET and a third FET. The equivalent resistor includes an oscillator, a fourth FET, a fifth FET and a capacitor connected to the fourth FET and the fifth FET. The oscillator is for generating a clock signal whose frequency is related to a charging and discharging capacitor in the oscillator to control charging and discharging of the capacitor in the equivalent resistance. The reference current outputting terminal is for outputting a reference current only related to a capacitance ratio of the capacitor to the charging and discharging capacitor. A reference current source system is further disclosed.