Abstract: Vacuum collector tube is a key component of concentrating collector of trough solar thermal system，heat loss directly affects system thermal efficiency.Impact on heat loss of inner diameter of heat-absorbing tube，external diameter of heat-absorbing tube and external diameter of glass tube were measured by using static balance method，results provided important parameters for heat-absorbing tube test.Experimental results showed that heat loss decreased and rate of decrease was faster as inner diameter of heat-absorbing tube greater.Heat loss increased and rate of increase was slower as external diameter of heat-absorbing tube greater.Heat loss basically remained unchanged with change of external diameter of glass tube.A set of relatively optimal parameters were selected based on experimental results with inner diameter of heat-absorbing tube of 62 mm，external diameter of heat-absorbing tube of 72 mm，external diameter of glass tube of 120 mm，heat loss of 12.95 W/m.Test parameters could provide theoretical basis for design of vacuum collector tube.