The invention discloses an auto-cascade heat pump with a middle throttling element and an adjusting method thereof. The heat pump comprises a single compressor, a condenser, an air-liquid separator, a condensing evaporator, an evaporator and a throttling valve, wherein non-azeotropic refrigerants containing two or more components are adopted as refrigerants. On the circulation basis of an original auto-cascade heat pump, the middle throttling element is added, the refrigerants at a condenser outlet, which are in a less dryness and undercooling state, can be used for eliminating the negative influence of condenser outlet state change caused by working condition changes on the system performance and taking the effect of obviously optimizing the performance by adjusting the mass flow ratio of the high-boiling point refrigerant and the low-boiling point refrigerant enriched in a middle throttling degree reasonable distribution system. The invention has the advantages of good suitability, simple structure, energy-saving operation and great working temperature difference.