The invention discloses an implement method and a device of called bear speech encryption in intersystem paging. The implement method includes a call establishment process which includes the following steps: A. a caller makes a call for a service mobile switching center; when the service mobile switching center judges that the call is intersystem paging for called enforced bear speech encryption,ISPAGE information is sent to a boundary mobile exchanging center, and the ISPAGE information is carried with confidential mode parameters; B. the boundary mobile exchanging center obtains called private long-code mask-code information by the confidential mode parameters and finishes the bear speech encryption of the called. The implement device comprises the service mobile switching center and the boundary mobile exchanging center. The service mobile switching center comprises a judge processing module. Based on the existing network structure, the invention resolves the problem that intersystem paging calling cannot carry out forced bear speech encryption of the called and has the advantages of small change of the existing network and good compatibility.