Claim 1: an Antibody or Antigen binding fragment comprising: at least six complementarity determining Regions (CDR) of the Antibody - 13654p afxi,13716p afxi afxi - or - 14； in which the Antibody heavy chain comprises a 13654p afxi - (HC) that has the Amino Acid Sequence shown in SEQ ID no. 18, 26,31 or 32 and a light chain (LC) that has the Amino Acid Sequence shown in SEQ ID no. 19； in the Antibody - 13716p afxi comprises a HC has the Amino Acid Sequence shown inSEQ ID no. 22, 27,33 or 34 and an LC has the Amino Acid Sequence shown in SEQ ID no. 23； in which the Antibody afxi - 14 includes a HC has the Amino Acid Sequence shown in SEQ ID no. 2528, 35 or 36 and an LC has the Amino Acid Sequence shown in SEQ ID no. 23； in which one or more of the six Cor has one, two or three substitutions, additions,Deletions of amino acids, or combinations thereof； andIn the Antibody or Antigen binding fragment binds to the Apple 2 domain of coagulation factor XI (FXI) and Inhibits the Activation of FXI.Claim 6: an Antibody or Antigen binding fragment that includes: (a) heavy chain (HC) that has a variable Domain comprises a complementarity Determining Region dAnd the heavy chain (HC - CDR) 1 which has the Amino Acid Sequence shown in SEQ ID no. 1, a HC - CDR 2 has the Amino Acid Sequence shown in SEQ ID no. 2:And a HC - CDR 3 has the Amino Acid Sequence shown in SEQ ID no. 3； (a) heavy chain (HC) that has a variable Domain comprises a HC - CDR 1 has the Amino Acid SequenceShown in SEQ ID no. 7, HC - CDR 2 has the Amino Acid Sequence shown in SEQ ID No. 8And a HC - CDR 3 has the Amino Acid Sequence shown in SEQ ID no. 9； or (b) heavy chain (HC) that has a variable Domain comprises a HC - CDR 1 that has the sequence of amino u00e1cidOs shown in SEQ ID no. 7, HC - CDR 2 has the Amino Acid Sequence shown in SEQ ID No. 8, and HC - CDR 3 has the Amino Acid Sequence shown in SEQ ID no. 13The variable Domain in which optionally includes 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 substitutions, addi
