The objective of this study is to determine the critical receiving power ratio (CRPR) of a receiving system fed only by high-voltage DC transmission lines. The approach is to check the voltage response when a severe fault occurs in a simplified asynchronously connected receiving system. The DC power limit is found by continuously increasing the DC power until the voltage cannot recover from the severe fault. The topic is expanded as follows. First, a simplified system model is established under a few reasonable assumptions. Then, the analytical voltage response expressions when a three-phase short-circuit fault occurs are developed, taking the effect of commutation failure, fast AC voltage control and load characteristics into consideration. The expressions of the DC power limits under different load characteristics are deduced from the analytical voltage response expressions. Besides, several crucial factors that limit the infeed power capacity of an asynchronously connected receiving system are discussed in this study based on the sensitivity analysis of the DC power limits. The CRPRs of a receiving system with different crucial characteristics are found through time-domain simulation with detailed models. The validity of the analytical voltage response expressions and the crucial factor analysis is well proved by the simulation results.