Abstract: The temperature distribution around an absorber tube in the single-phase water region, saturated region and dry steam region of a direct steam generation(DSG) solar collector was studied at steady state along circumferential direction by numerical calculations, based on which the heat loss model of collector was established, while the influence of following factors on the heat loss in different phase regions of absorber analyzed, such as the fluid temperature, mass flow-rate and working pressure, etc. Results show that fluid temperature is the key factor influencing the heat loss of collector, which rises with increasing temperature difference between fluid and ambient air; working pressure and mass flow rate of fluid have little influences on the heat loss.