Cut the pork tenderloin into large slices (about 10cm*6cm*0.3cm). Cut the scallion into thin slices, and the ginger into thin strips. Sock the scallion and ginger with a little water for 30 minutes to make scallion-and-ginger water. Add the scallion-and-ginger water, the rice win and 1g salt to the pork slices, stir until fully absorbed and the meat becomes sticky. Add water little by little to the corn starch to make a stick paste. Then add a little vegetable oil and blend. Heat the large amount of oil into a frying pan. Dress the pork slice with the starch paste evenly, and fry in the oil, until the meat surface becomes crisp. Take out the pork and heat the oil again, fry the meat for a second time – essential step. Remove most remaining oil in the pan and leave a little. Add 20ml water, the vinegar, the soy sauce, the sugar and 1g salt, heat to make sweet and sour sauce. Add the fried meat slices into the sauce, sauté in strong fire for 1 minute to make the sauce evenly wrap the meat.