An anti-CLD18A2 VHH, wherein a complementarity determining region CDR of the anti-CLD18A2 VHH comprises CDR1-CDR3 having amino acid sequences as shown below: CDR1 having an amino acid sequence represented by SEQ ID NO. 4, CDR2 having an amino acid sequence represented by SEQ ID NO. 19, and CDR3 having an amino acid sequence represented by SEQ ID NO. 33; or CDR1 having an amino acid sequence represented by SEQ ID NO. 5, CDR2 having an amino acid sequence represented by SEQ ID NO. 20, and CDR3 having an amino acid sequence represented by SEQ ID NO. 34; or CDR1 having an amino acid sequence represented by SEQ ID NO. 6, CDR2 having an amino acid sequence represented by SEQ ID NO. 21, and CDR3 having an amino acid sequence represented by SEQ ID NO. 35; or CDR1 having an amino acid sequence represented by SEQ ID NO. 7, CDR2 having an amino acid sequence represented by SEQ ID NO. 22, and CDR3 having an amino acid sequence represented by SEQ ID NO. 36; or CDR1 having an amino acid sequence represented by SEQ ID NO. 8, CDR2 having an amino acid sequence represented by SEQ ID NO. 23, and CDR3 having an amino acid sequence represented by SEQ ID NO. 37; or CDR1 having an amino acid sequence represented by SEQ ID NO. 9, CDR2 having an amino acid sequence represented by SEQ ID NO. 24, and CDR3 having an amino acid sequence represented by SEQ ID NO. 38; or CDR1 having an amino acid sequence represented by SEQ ID NO. 10, CDR2 having an amino acid sequence represented by SEQ ID NO. 25, and CDR3 having an amino acid sequence represented by SEQ ID NO. 36; or CDR1 having an amino acid sequence represented by SEQ ID NO. 11, CDR2 having an amino acid sequence represented by SEQ ID NO. 26, and CDR3 having an amino acid sequence represented by SEQ ID NO. 39. CDR1 having an amino acid sequence represented by SEQ ID NO. 4, CDR2 having an amino acid sequence represented by SEQ ID NO. 19, and CDR3 having an amino acid sequence represented by SEQ ID NO. 33; or CDR1 having an amino acid sequence represented by SEQ ID NO. 5, CDR2 having an amino acid sequence represented by SEQ ID NO. 20, and CDR3 having an amino acid sequence represented by SEQ ID NO. 34; or CDR1 having an amino acid sequence represented by SEQ ID NO. 6, CDR2 having an amino acid sequence represented by SEQ ID NO. 21, and CDR3 having an amino acid sequence represented by SEQ ID NO. 35; or CDR1 having an amino acid sequence represented by SEQ ID NO. 7, CDR2 having an amino acid sequence represented by SEQ ID NO. 22, and CDR3 having an amino acid sequence represented by SEQ ID NO. 36; or CDR1 having an amino acid sequence represented by SEQ ID NO. 8, CDR2 having an amino acid sequence represented by SEQ ID NO. 23, and CDR3 having an amino acid sequence represented by SEQ ID NO. 37; or CDR1 having an amino acid sequence represented by SEQ ID NO. 9, CDR2 having an amino acid sequence represented by SEQ ID NO. 24, and CDR3 having an amino acid sequence represented by SEQ ID NO. 38; or CDR1 having an amino acid sequence represented by SEQ ID NO. 10, CDR2 having an amino acid sequence represented by SEQ ID NO. 25, and CDR3 having an amino acid sequence represented by SEQ ID NO. 36; or CDR1 having an amino acid sequence represented by SEQ ID NO. 11, CDR2 having an amino acid sequence represented by SEQ ID NO. 26, and CDR3 having an amino acid sequence represented by SEQ ID NO. 39.