A sinus dental implant for implanting into an alveolar hole on a patient's upper gum, comprising: a main body having two opposite ends defined as a drilling end and a connection end, and an embedment peripheral surface extended from the drilling end toward the connection end; and the drilling end having an outer peripheral area formed into a drilling zone capable of contacting with a bottom of the alveolar hole and a sunken central area formed into a recess surrounded by the drilling zone; an external thread being formed on the embedment peripheral surface of the main body to extend in a first spiral direction for engaging with a side wall surface of the alveolar hole; and a plurality of spiral cutting flutes being formed on the main body and the external thread to extend from the drilling zone toward the connection end in a second spiral direction, which is opposite to the first spiral direction, and a cut being formed between every spiral cutting flute and the recess for communicating the spiral cutting flute with the recess; wherein the drilling zone is divided by the spiral cutting flutes into a plurality of drilling segments that are circumferentially spaced along the recess; the sinus dental implant being characterized in that every drilling segment has a lowest portion defined as a lower drilling portion, the drilling segment rises gradually from the lower drilling portion of the drilling segment toward one of the spiral cutting flutes to form an upper drilling portion, so that a guide surface is formed between the lower drilling portion and the upper drilling portion while a guide space is also formed between the lower drilling portion and the upper drilling portion to communicate with the recess and the spiral cutting flute. a main body having two opposite ends defined as a drilling end and a connection end, and an embedment peripheral surface extended from the drilling end toward the connection end; and the drilling end having an outer peripheral area formed into a drilling zone capable of contacting with a bottom of the alveolar hole and a sunken central area formed into a recess surrounded by the drilling zone; an external thread being formed on the embedment peripheral surface of the main body to extend in a first spiral direction for engaging with a side wall surface of the alveolar hole; and a plurality of spiral cutting flutes being formed on the main body and the external thread to extend from the drilling zone toward the connection end in a second spiral direction, which is opposite to the first spiral direction, and a cut being formed between every spiral cutting flute and the recess for communicating the spiral cutting flute with the recess; wherein the drilling zone is divided by the spiral cutting flutes into a plurality of drilling segments that are circumferentially spaced along the recess; the sinus dental implant being characterized in that every drilling segment has a lowest portion defined as a lower drilling portion, the drilling segment rises gradually from the lower drilling portion of the drilling segment toward one of the spiral cutting flutes to form an upper drilling portion, so that a guide surface is formed between the lower drilling portion and the upper drilling portion while a guide space is also formed between the lower drilling portion and the upper drilling portion to communicate with the recess and the spiral cutting flute.