Abstract: The compliance of the thermal flow field quality of the large icing wind tunnel is the foundation of its airworthiness application. In order to understand the effects of upgrading of the refrigeration system on the thermal flow field quality in the CARDC icing wind tunnel, a comprehensive verification test is carried out for the main test section. Then, the thermal flow field qualities, both at the exit of the heat exchanger and in the test section, are evaluated. Finally, the correction relationship of the airflow total temperature and the thermal flow field operating envelop are achieved. Results show that the thermal flow field qualities, both at the exit of the heat exchanger and in the test section, are better than the quality index given in SAE ARP5905, under the main test conditions. Compared with the test results in 2019, the spatial uniformity in the model area of the test section is greatly enhanced. Particularly, non-uniform temperature peak points exceeding the standard in the model area are eliminated under the conditions of high airspeed and low total temperature. Finally, the upgrading of the refrigeration system in 2020 greatly extends the thermal flow field operating envelop, so that the temperature simulation capability of the CARDC icing wind tunnel is enhanced significantly.