A 3-plate mold assembly with a common mold base comprises: a stationary mold mounted on a fixed side of an injection molding machine and a movable mold mounted on a movable side of the injection molding machine. The stationary mold comprises a stationary-side fixed plate on which are disposed four pillars to be inserted through a stripper and into a female insert assembly. When new products need to be produced, it only needs to replace the female and male insert and the rest parts of the stationary and movable molds don't need to be replaced, thus substantially saving production cost.