A method for determining a paging slot of a Code Division Multiple Access, CDMA, mobile station trunking service, wherein when the mobile station supports minus slot function, the method comprises: if a system identifier and a network identifier of a base station do not match with any one in a system identifier and a network identifier list stored in the mobile station, the mobile station calculating a paging slot according to a slot cycle index which is a value not more than the smaller of a max slot cycle index and 1; otherwise, if the mobile station receives minus slot paging cycle information on a paging channel overhead message, and the mobile station has stored a Push To Talk, PTT, slot cycle index, the mobile station calculating the paging slot by obtaining a minimal value from a max PTT slot cycle index, the PTT slot cycle index, the max slot cycle index, and a slot cycle index; if the mobile station receives the minus slot paging cycle information on the paging channel overhead message, but the mobile station has not stored a PTT slot cycle index, the mobile station calculating the paging slot by obtaining a minimal value from the max PTT slot cycle index, the max slot cycle index, and the slot cycle index; if the mobile station does not receive the minus slot paging cycle information on the paging channel overhead message, but the mobile station has stored a PTT slot cycle index, the mobile station calculating the paging slot by obtaining a minimal value from the PTT slot cycle index, the max slot cycle index, and the slot cycle index; and if the mobile station does not receive the minus slot paging cycle information on the paging channel overhead message, and the mobile station has not stored a PTT slot cycle index, the mobile station calculating the paging slot by obtaining a minimal value from the max slot cycle index and the slot cycle index. if a system identifier and a network identifier of a base station do not match with any one in a system identifier and a network identifier list stored in the mobile station, the mobile station calculating a paging slot according to a slot cycle index which is a value not more than the smaller of a max slot cycle index and 1; otherwise, if the mobile station receives minus slot paging cycle information on a paging channel overhead message, and the mobile station has stored a Push To Talk, PTT, slot cycle index, the mobile station calculating the paging slot by obtaining a minimal value from a max PTT slot cycle index, the PTT slot cycle index, the max slot cycle index, and a slot cycle index; if the mobile station receives the minus slot paging cycle information on the paging channel overhead message, but the mobile station has not stored a PTT slot cycle index, the mobile station calculating the paging slot by obtaining a minimal value from the max PTT slot cycle index, the max slot cycle index, and the slot cycle index; if the mobile station does not receive the minus slot paging cycle information on the paging channel overhead message, but the mobile station has stored a PTT slot cycle index, the mobile station calculating the paging slot by obtaining a minimal value from the PTT slot cycle index, the max slot cycle index, and the slot cycle index; and if the mobile station does not receive the minus slot paging cycle information on the paging channel overhead message, and the mobile station has not stored a PTT slot cycle index, the mobile station calculating the paging slot by obtaining a minimal value from the max slot cycle index and the slot cycle index.