The invention provides a manufacturing method for biaxial extension polyamide resin. When processing the biaxial extension for the sheets which are not extended via the expander-type biaxial stretch-forming machine, the surface crystallization index measured by the full-reflection FT-IR method for the sheets which are not extended before being provided to the expander is below 1-0; the sheets which are not extended is formed by the fusing polyamide resin via a squeezer; in order to achieve the purpose, the fusing polyamide resin by the squeezer is pressed on a cooling drum at 15-30 centigradeto obtain the sheets which are not extended; the fusing polyamide resin is dipped in warm water at 30-49 centigrade for more than 5 second and dipped in warm water at 50-65 centigrade for 60-150 seconds to make the water absorbing rate as 3.0-7.0 quality%; then the method processes the simultaneous biaxial extension in the expander-type biaxial stretch-forming machine.