The invention discloses an adjustable trolley for section tunnel construction and an adjustment method. The trolley comprises a template system and a mobile supporting system capable of longitudinally move back and forth in a constructed tunnel, wherein the template system comprises multiple arch templates and left and right side templates which are distributed symmetrically; the two side templates and one arch template are spliced to form a forming template; the arch templates are integrated templates or assembled templates; the mobile supporting system comprises a main beam, a lower part supporting structure, a vertical supporting structure and left and right side part supporting structures. The adjustment method comprises the following steps: 1, removing the arch templates; 2, adjusting the vertical supporting structure; 3, connecting and reinforcing the arch templates; 4, reinforcing the side templates and adjusting an auxiliary supporting frame; 5, laterally moving the side templates and splicing the forming templates. The adjustable trolley disclosed by the invention is reasonable in design, easy and convenient to use and operate and good in use effect, can be easily adjusted to meet the demand for secondary lining construction of a tunnel with a suddenly changed section, can save labor and time, and is high in safety, economical and practical.