Abstract: The performance of the fluxgate sensor in open-loop measurement mode as a function of temperature was investigated. To avoid the mutual coupling effects between the circuit and the sensor during the closed-loop signal processing of the fluxgate, an open-loop magnetic field measurement system for the fluxgate was developed, the results of which directly reflect the intrinsic physical properties of the fluxgate sensor. Based on the characteristics of different performance parameters of the fluxgate sensor, a temperature cycling test in a non-magnetic environment was designed and conducted within the temperature range of -40°C to +80°C. The test results showed that the offset drift of the fluxgate sensor did not exceed ±1.5 nT, the amplitude of signal phase drift reached 60°, the open-loop gain changed by approximately ±5%, and the noise varied between 4 pT/√Hz and 7 pT/√Hz@1Hz. It can be seen that, except for the phase characteristics of the sensor signal, the fluxgate sensor exhibits excellent temperature stability. In the closed-loop control circuit of a sensor, the phase-sensitive demodulation link is highly sensitive to signal phase. Significant phase drift is the main factor causing the temperature drift of the fluxgate magnetometer.