A method for determining a paging slot by a base station for CDMA trunking service, comprising: when the base station determines a mobile station operates in a slotted mode: if the base station determines the PTT version number of a mobile station is greater than or equal to a preset value, and the base station has obtained a negative slot cycle index of the mobile station, then the base station choosing the minimum value among max PTT slot cycle index, PTT slot cycle index, max slot cycle index and slot cycle index as the first slot cycle index, and paging the mobile station in the slot cycle determined by the first slot cycle index; if the base station determines the PTT version number of the mobile station is greater than or equal to the preset value, and the base station has not obtained the negative slot cycle index of the mobile station, the base station choosing the minimum value among the max PTT slot cycle index, the max slot cycle index and the slot cycle index as the second slot cycle index, and paging the mobile station in the slot cycle determined by the second slot cycle index; and if the base station determines the PTT version number of the mobile station is smaller than the preset value, the base station choosing the minimum value of the max slot cycle index and the slot cycle index as the third slot cycle index, and paging the mobile station in the slot cycle determined by the third slot cycle index; when the base station is unable to determine whether the mobile station operates in a slotted mode or not, or unable to determine the slot cycle index of the mobile station, setting a value of the slot cycle index as 1 and then paging the mobile station according to the foregoing three methods. when the base station determines a mobile station operates in a slotted mode: if the base station determines the PTT version number of a mobile station is greater than or equal to a preset value, and the base station has obtained a negative slot cycle index of the mobile station, then the base station choosing the minimum value among max PTT slot cycle index, PTT slot cycle index, max slot cycle index and slot cycle index as the first slot cycle index, and paging the mobile station in the slot cycle determined by the first slot cycle index; if the base station determines the PTT version number of the mobile station is greater than or equal to the preset value, and the base station has not obtained the negative slot cycle index of the mobile station, the base station choosing the minimum value among the max PTT slot cycle index, the max slot cycle index and the slot cycle index as the second slot cycle index, and paging the mobile station in the slot cycle determined by the second slot cycle index; and if the base station determines the PTT version number of the mobile station is smaller than the preset value, the base station choosing the minimum value of the max slot cycle index and the slot cycle index as the third slot cycle index, and paging the mobile station in the slot cycle determined by the third slot cycle index; when the base station is unable to determine whether the mobile station operates in a slotted mode or not, or unable to determine the slot cycle index of the mobile station, setting a value of the slot cycle index as 1 and then paging the mobile station according to the foregoing three methods. if the base station determines the PTT version number of a mobile station is greater than or equal to a preset value, and the base station has obtained a negative slot cycle index of the mobile station, then the base station choosing the minimum value among max PTT slot cycle index, PTT slot cycle index, max slot cycle index and slot cycle index as the first slot cycle index, and paging the mobile station in the slot cycle determined by the first slot cycle index; if the base station determines the PTT version number of the mobile station is greater than or equal to the preset value, and the base station has not obtained the negative slot cycle index of the mobile station, the base station choosing the minimum value among the max PTT slot cycle index, the max slot cycle index and the slot cycle index as the second slot cycle index, and paging the mobile station in the slot cycle determined by the second slot cycle index; and if the base station determines the PTT version number of the mobile station is smaller than the preset value, the base station choosing the minimum value of the max slot cycle index and the slot cycle index as the third slot cycle index, and paging the mobile station in the slot cycle determined by the third slot cycle index; when the base station is unable to determine whether the mobile station operates in a slotted mode or not, or unable to determine the slot cycle index of the mobile station, setting a value of the slot cycle index as 1 and then paging the mobile station according to the foregoing three methods.