A heat pump system and a defrosting control method therefor are provided. The defrosting control method comprises: in S100, initializing a first default parameter TM n and a second default parameter TN n in a preset defrosting interval indicatrix X when a heat pump system runs, wherein the preset defrosting interval indicatrix X=T 1 /TM n +T 2 /TN n , T 1 represents a running time of the heat pump system when an outdoor temperature is greater than or equal to an outdoor temperature preset value, T 2 represents a running time of the heat pump system when the outdoor temperature is less than the outdoor temperature preset value, and n represents the number of executed defrosting cycles; in S200, executing the defrosting cycle when the preset defrosting interval indicatrix X is greater than or equal to a preset constant value, and terminating the defrosting cycle after a defrosting cycle exit condition is met; in S300, obtaining an actual time spent on the defrosting cycle; in S400, comparing the actual time spent on the defrosting cycle with an expected defrosting time, and adjusting the first default parameter and the second default parameter when the actual defrosting time deviates from the expected defrosting time; and in S500, repeating steps S200 to S400. The heat pump system and the defrosting control method therefor according to this application can adjust a defrosting interval according to an actual application situation and achieve a balance between unit performance and comfort degree of customers.