A pile-bottom grouting cavity device, comprising: a grouting capsule, having an expansion state in which an interior of the grouting capsule is filled with grout to bear a pile body, and a contracted state in which an interior of the grouting capsule is hollow; a grouting pipe, communicated with an inner cavity of the grouting capsule for grouting the grouting capsule, and a fixing plate, provided with the grouting capsule thereon, and a through hole therethrough, wherein the through hole is to be communicated with a bottom of a accommodation hole for allowing slurry and/or sediment within the accommodation hole to pass through the through hole of the fixing plate, wherein the pile-bottom grouting cavity device further comprises a grout replenishing structure which communicates with the through hole for grouting into the through hole, wherein, the grout replenishing structure comprises at least one grout replenishing tube which is communicated with the through hole for grouting into the through hole; characterized in that the fixing plate has a grout-storage chamber communicated with the through hole, and the grout replenishing tube is communicated with a grout inlet of the grout-storage chamber, wherein preferably, the grout replenishing tube has a second grouting portion extending into a cavity of the through hole and provided with a plurality of second grouting holes, and the second grouting portion is an arcuate tube extending along a hole wall contour of the through hole, more preferably, the second grouting portion is an annular pipe extending along the contour of the hole wall of the through hole. a grouting capsule, having an expansion state in which an interior of the grouting capsule is filled with grout to bear a pile body, and a contracted state in which an interior of the grouting capsule is hollow; a grouting pipe, communicated with an inner cavity of the grouting capsule for grouting the grouting capsule, and a fixing plate, provided with the grouting capsule thereon, and a through hole therethrough, wherein the through hole is to be communicated with a bottom of a accommodation hole for allowing slurry and/or sediment within the accommodation hole to pass through the through hole of the fixing plate, wherein the pile-bottom grouting cavity device further comprises a grout replenishing structure which communicates with the through hole for grouting into the through hole, wherein, the grout replenishing structure comprises at least one grout replenishing tube which is communicated with the through hole for grouting into the through hole; characterized in that the fixing plate has a grout-storage chamber communicated with the through hole, and the grout replenishing tube is communicated with a grout inlet of the grout-storage chamber, wherein preferably, the grout replenishing tube has a second grouting portion extending into a cavity of the through hole and provided with a plurality of second grouting holes, and the second grouting portion is an arcuate tube extending along a hole wall contour of the through hole, more preferably, the second grouting portion is an annular pipe extending along the contour of the hole wall of the through hole.