This paper designed a kind of circulating solar heat collection tubes (CSHT) for a cyclic desalination system. CSHT was consist of tubes with vacuum layer, I-shaped and U-shaped connectors. In order to analyze the influence of factors of solar intensity (I), inlet fluid temperature (Ti), inlet velocity (u) and tube diameter (D) on the thermal performance of CSHT, phase transformation process in tubes was simulated by FLUENT, and User-Defined Functions of mass and heat source terms were introduced. Results showed outlet temperature and vapor mass fraction were both positively correlated with I and Ti, but negatively correlated with u and D. Then sensitivity analysis was introduced and conducted for ranking the factors, and their average sensitivity values were in descending order of I, D, u, Ti. Under orthogonal test, three optimal schemes (D = 25 mm) of simulation were picked out, and their average heat collection efficiency and exergy efficiency were 81.31% and 77.50%, respectively. Finally, similarity criterion was applied to transmit information of quantitative data from experimental model to corresponding prototype. Through similarity criteria analysis, three optimal schemes were obtained under the condition of tube diameter is 37 mm (diameter is 25 mm in numerical simulation). Optimal operation velocities can be 0.097 m/s, 0.127 m/s and 0.164 m/s respectively in the pilot of CSHT, under the solar intensity values of 800 W/m2, 1000 W/m2 and 1200 W/m2.