The invention discloses a concave measuring mark assembly and a mounting and measuring method, and relates to the field of measuring signs. The concave measuring sign assembly comprises a measuring sign; the measuring sign comprises a hollow tray and a drop ball located below the tray; the tray basically takes a hemispherical shape with an opening upward, and the drop ball is basically connected to the center of the bottom of the tray by a fall line. The concave measuring mark assembly is relatively high in mounting precision and is relatively high in fixing property during use.