The invention provides a forming method for a crystal oscillator. The forming method comprises the steps that a first substrate is provided, and the first substrate is provided with a first surface and a second surface opposite to the first surface; the first substrate is etched along the first surface to form a vacuum cavity and an external opening, wherein the depth of the vacuum cavity is smaller than the depth of the external opening; a second substrate is provided, and the surface of the second substrate is provided with an oscillation crystal; the first substrate and the second substrate are bonded, and the vacuum cavity directly faces the oscillation crystal; the first substrate is thinned along the second surface, wherein the depth of the external opening is subtracted from the thickness of the first substrate; the thickness of the first substrate is thinned; the depth of the vacuum cavity is subtracted from the thickness of the first substrate. According to the forming method for the crystal oscillator, the process is simple, and a process window is wide.