To address the calibration demand for the response time constant of fast-response K-type thermocouples under gas medium conditions, a calibration device based on the gas temperature step method was developed. Key parameters including heater power, orifice area, and nozzle flow rate were determined via theoretical calculations, and Ansys Fluent software was utilized for simulation to optimize the structure of the step temperature generation module. A calibration method based on synchronous dynamic pressure monitoring was proposed, which takes the pressure step moment as the reference to eliminate non-ideal excitation interference and ensure the calculation accuracy of the response time constant. Experimental tests were conducted using the developed device, and the results indicate that the gas temperature step amplitude generated by the device exceeds 200 ℃ with a temperature step excitation time of approximately 2.2 ms. The device can effectively calibrate the response time constant of K-type thermocouples with different wire diameters, demonstrating significant engineering application value.