The cryogenic fluids’ flow performance and condensation characteristics with different heating powers in cryogenic loop heat pipes (CLHPs) have not been studied due to the difficulty of measurement at low temperature. In this study, a test system was designed and fabricated to characterize the condensation flow patterns of propylene CLHP and its heat transfer performance with different heating powers. The results show that the two-phase region length and flow pattern in the condenser were closely related to the operation mode of the CLHP. The vapor front in the condenser oscillated at the condenser inlet at a low heating power, which resulted in an unstable operation of the CLHP. Moreover, by comparing the condensation heat transfer coefficient (HTC) with the condensation correlations, the Cavallini correlation is recommended for the design of the CLHP condenser.