In order to verify the insulation features and anti-freezing protection effect of all-glass evacuated tube collector, the fluid temperature in solar collector and its changing were tested experimentally in static conditions in winter night, and the heat dissipation and the average heat loss coefficient were calculated as well. The heat loss characteristics and the changing regulations were analyzed in detail. Results indicated that the lowest fluid temperature was ranged from 8 ℃ to 25 ℃, and the temperature drop rate was between 0.7 ℃/h and 1.3 ℃/h. The total amount of heat dissipation was about 1 800-4 700 kJ, and the average heat loss coefficient was 0.427 W/(m²·K) during the testing nights. The study of the heat dissipation of solar collector and the changing of the lowest fluid temperature in it, can effectively demonstrate its insulation properties, which can provide evidence for the anti-freezing of solar collector and its outdoor pipe loops in severe cold areas.