The invention relates to a one-pile and one-column construction method, which is applied to horizontal extension construction of existing underground space. The method comprises the following steps ofS1, using the existing underground space as a working well for box culvert jacking, and carrying out the construction of box culvert jacking as the construction work space; S2, measuring the positions of one column and one pile according to a drawing, and then forming holes at the corresponding positions of a box culvert top plate and a box culvert bottom plate; S3, constructing a first section pile at the hole of the box culvert bottom plate, then constructing reversely a first section column on the first section pile, then carrying out two-way synchronous construction of one pile and one column repeatedly in sequence, and stopping construction of the column when the height of the column reaches the top plate of thefloorB1;and S4,carrying out pile grouting after completion of the one-column and one-pile construction. The invention also provides a pile-pressing mechanism, which is applied to the one-pile and one-column construction method. The operation of the existing structure upperspace is not affected while maintaining the original appearance of a completed building, and the underground construction space is created and fully utilized to realize the one-pile and one-column construction.