A fan dynamic pressure structure having a plastic frame integrally formed around an oil-containing sintered metal powder bearing , characterized by comprising: an oil-containing sintered metal powder bearing having a bushing body , wherein the bushing body has a shaft hole in a center thereof; a plastic frame having a middle tube and a chassis , the middle tube integrally formed around a peripheral of the bushing body ; a fan assembly having a plurality of fan blades and an axial shaft , wherein the axial shaft is disposed in a center of the fan assembly and the axial shaft penetrates through the shaft hole of the oil-containing sintered metal powder bearing and protrudes downwards, and the axial shaft comprises an annular groove ; and characterized in that the fan dynamic pressure structure further comprises an annular dynamic pressure piece having an insertion hole and an annular body surrounding the insertion hole , wherein the insertion hole is fixed in the annular groove of the fan assembly , and the annular body has a plurality of curved radial dynamic pressure ditches formed on a surface, adjacent to the oil-containing sintered metal powder bearing , of the annular body , wherein the axial shaft comprises a cone end portion at an end portion of the axial shaft , and the cone end portion comprises an inclined surface , and the insertion hole of the annular dynamic pressure piece comprises an edge wall , on an inner wall of the insertion hole , corresponding to the inclined surface , wherein the edge wall of the annular dynamic pressure piece misaligns with the inclined surface of the axial shaft after the insertion hole engaged with the annular groove . an oil-containing sintered metal powder bearing having a bushing body , wherein the bushing body has a shaft hole in a center thereof; a plastic frame having a middle tube and a chassis , the middle tube integrally formed around a peripheral of the bushing body ; a fan assembly having a plurality of fan blades and an axial shaft , wherein the axial shaft is disposed in a center of the fan assembly and the axial shaft penetrates through the shaft hole of the oil-containing sintered metal powder bearing and protrudes downwards, and the axial shaft comprises an annular groove ; and characterized in that the fan dynamic pressure structure further comprises an annular dynamic pressure piece having an insertion hole and an annular body surrounding the insertion hole , wherein the insertion hole is fixed in the annular groove of the fan assembly , and the annular body has a plurality of curved radial dynamic pressure ditches formed on a surface, adjacent to the oil-containing sintered metal powder bearing , of the annular body , wherein the axial shaft comprises a cone end portion at an end portion of the axial shaft , and the cone end portion comprises an inclined surface , and the insertion hole of the annular dynamic pressure piece comprises an edge wall , on an inner wall of the insertion hole , corresponding to the inclined surface , wherein the edge wall of the annular dynamic pressure piece misaligns with the inclined surface of the axial shaft after the insertion hole engaged with the annular groove . <EOS>