A process of fabricating a non-gap 3-D microstructure array mold core comprises a first step in which a buffer layer is coated on a substrate. A photomask layer is then coated of the buffer layer. A pattern is subsequently formed on the photomask by photo-lithography. The patterned photomask layer is subjected to a reflow by which a microstructure array is formed on the photomask layer. The microstructure array is coated with a metal conductive layer. The microgaps of the microstructure array are eliminated by an electrocasting layer which is coated on the microstructure array. The non-gap microstructure array mold core so fabricated is made into a metal molding tool by microinjection molding or microthermo-pressure molding.