TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Components: The method includes further three modes to control the operational parameters. The fourth mode obtains a total value of sonic planar module measured by the method B to be higher than 470 daN/mm2 and a hydrolysis resistance measured in a PCT test for 36 hours at 125 degrees C and at a retention rate of elongation at fracture to be higher than 70%, where the biaxial stretching is implemented by: carrying out longitudinal stretching at the stretching rate in an order of 2-6 or 2.5-5 or 2.9-4.5 and at a stretching temperature in an order of 70-150 degrees C or 85-140 degrees C or 90-135 degrees C; carrying out transverse stretching at the stretching rate in an order of 2-6 or 3.5-5 or 3.9-4.5 and at a stretching temperature in an order of 95-150 degrees C or 105-145 degrees C or 110-140 degrees C; and including surface stretching (rate of longitudinal stretchingx rate of transverse stretching) in an order of 4-25 or 7-25 or 11-25. The fifth mode obtains a total value of sonic planar module measured by the method B to be 440-470 daN/mm2 and a hydrolysis resistance measured in a PCT test for 36 hours at 125 degrees C and at a retention rate of elongation at fracture to be 50-70%, where the biaxial stretching is implemented by: carrying out longitudinal stretching at the stretching rate of 2-6 or 2.5-5 and at a stretching temperature in an order of 70-150 degrees C or 90-140 degrees C; carrying out transverse stretching at the stretching rate of 2-6 or 3.5-5 and at a stretching temperature in an order of 95-150 degrees C or 110-145 degrees C; and including surface stretching (rate of longitudinal stretchingx rate of transverse stretching) of 4-20. The sixth mode obtains a total value of sonic planar module measured by the method B to be lower than 440 daN/mm2 and a hydrolysis resistance measured in a PCT test for 36 hours at 125 degrees C and at a retention rate of elongation at fracture to be lower than 50%, where the biaxial stretching is implemented by: carrying out longitudinal stretching at the stretching rate of 2-6 and at a stretching temperature in an order of 85-150 degrees C or 95-145 degrees C; carrying out transverse stretching at the stretching rate of 2-6 and at a stretching temperature in an order of 105-150 degrees C or 110-150 degrees C; and including surface stretching (rate of longitudinal stretchingx rate of transverse stretching) of 4-12.