The invention discloses an adjustable reserved hole constructing mold and constructing method. The adjustable reserved hole constructing mold comprises an outer mold, a horizontal bottom plate and an upper covering plate, wherein the horizontal bottom plate is located at the bottom of the inner side of the outer mold, the upper covering plate is installed on the upper part of the outer mold in a covering mode, and the upper covering plate is a round covering plate; the outer mold comprises a vertical cylinder, a horizontal base plate and an annular covering opening; and an eccentric hole is formed in the horizontal bottom plate for passing through of installed pipelines. The adjustable reserved hole constructing method comprises the following steps of step 1, supporting formwork of a cast-in-place slab; step 2, surveying a line of the pipeline installing position; step 3, fixing of the outer mold; step 4, constructing of the cast-in-place slab; step 5, installing of the horizontal bottom plate; step 6, installing of the pipeline; and step 7, sealing and blocking of a hole opening. According to the adjustable reserved hole constructing mold and constructing method, design is reasonable, construction is simple and convenient, and the using effect is good; and the position of through-floorslab pipeline can be adjusted through the horizontal bottom plate with the eccentric holes to guarantee installing precision of the pipeline, and the problems, existing in current reserved hole construction, that working process is complex, potential safety hazards exist in high altitude formwork supporting, and sealing and blocking quality of the hole opening is hard to be guaranteed can be effectively solved.