The invention provides an adjustable block gauge, which is a measuring tool for measuring flatness or straightness and comprises an upper wedge block, a lower wedge block and an insertion strip. The adjustable block gauge has the advantages that the structure is simple, the operation is simple when the block gauge is used in combination with a flat rule and three gauge blocks with the same thickness, the measuring accuracy is high, the measuring speed is high, the effects of economy and durability are realized, the application range is wide and the like.