The embodiment of the invention provides single-lithium-ion conductive polymer lithium salt, the structural formula of which is shown as a formula (I), wherein Y is -N-C(=O)-R1- or -N-S(=O)2-R2-, R1 and R2 are respectively selected from alkylene, halogenated alkylene, alkyleneoxy, halogenated alkyleneoxy, alkenylene, halogenated alkenylene, alkenylidenoxy, halogenated alkenylidenoxy, arylene, halogenated arylene, arylidenoxy and halogenated arylidenoxy; z1, Z2, Z3, Z4 and Z5 are respectively selected from fluorine, chlorine, bromine, alkyl, halogenated alkyl, alkoxy, halogenated alkoxy, alkenyl, halogenated alkenyl, alkenyl, halogenated alkenyl, aryl, halogenated aryl, aryloxy and halogenated aryloxy. The lithium salt has flame-retardant and single-lithium-ion conductive characteristics, and the safety performance, cycle performance and rate capability of the battery can be improved. The invention also provides a lithium secondary battery electrolyte and a lithium secondary battery.