For the gas calibrator with dynamic dilution ratio of gas, the change of temperature will affect the density of gas, thus affecting the mass flow rate through the mass flow controller. If the temperature dilution ratio cannot be collected in real time, there will be a large error. In this paper, a four-wire temperature sensor PT100, an external excitation constant-current source, an anti-mixing filter circuit and a 24-bit DELta-sigma ADC are used to measure the temperature in a gas chamber. The constant-current source excitation PT100 converts the temperature signal into a voltage signal, and then into a digital signal through the Delta-sigma ADC. Finally, the data is collected by FPGA and stored in Nor Flash chip. The experimental results show that the temperature resolution of the designed system can reach 0.005℃, the repeatability is good, and the problems of lead resistance, self-heating effect and small temperature measurement range are solved, which has certain engineering application value.