The invention relates to the field of civil engineering and particularly relates to an automatic compaction device and a compaction molding technology adopting the automatic compaction device and applied to a permeable cement concrete beam specimen. The automatic compaction device comprises a test mold, a compaction platform, a limiting bolt, a compaction hammer, a compaction rod, a limiting ring, a rack, a drive cavity, a fixed bolt and a reset rod, wherein a special-shaped gear in the drive cavity is divided into a tooth slot part and a toothless slot part; the tooth slot part is in contact with the compaction rod; the compaction hammer is lifted and rotated to the toothless slot part to be in contact with the compaction rod; the compaction hammer freely falls off to complete compaction; compaction work is controlled through adjusting weight of the compaction hammer and changing the radius of the special-shaped gear; and concrete aggregate is filled by adopting layered film filling and layered inserting and tamping methods. The automatic compaction device has the advantages that the concrete aggregate is good in inserting and tamping effect, the device is simple in operation, the compacted and molded permeable cement concrete beam specimen is good in molding effect and high in qualified rate, and subsequent fracture resistance test of the beam specimen and freezing and thawing test are facilitated.