A method for manufacturing a secondary battery, the method comprising: a forming step of pressing a pouch sheet by using a press die so that left and right accommodation grooves (121, 122), which are bilaterally symmetrical to each other and are opened upward, and a bridge connecting the left and right accommodation grooves (121, 122) to each other are formed in the pouch sheet to form a pouch sheet so that an electrode assembly is accommodated; and a folding step of seating the electrode assembly on one of the left and right accommodation grooves (121, 122) to fold the electrode assembly so that the left and right accommodation grooves (121, 122) face each other, wherein, in the forming step, the pouch sheet is formed so that the bridge protrudes upward with respect to bottom surfaces (128, 129) of the left and right accommodation grooves, and a curved portion having a rounded shape is formed on an upper end of the bridge, characterized in that in the forming step, a first bending part having a shape in which outer side surfaces of the left and right accommodation grooves (121, 122) are respectively bent downward with respect to outer circumferential surfaces (124, 125) of the pouch sheet is formed with a first curved surface having a rounded shape, a second bending part having a shape in which the outer side surfaces of the left and right accommodation grooves (121, 122) are respectively bent upward with respect to the bottom surfaces (128, 129) of the left and right accommodation grooves is formed with a second curved surface having a rounded shape, and the pouch sheet is formed so that a clearance (c) of each of inflection surfaces (126, 127) formed between the first curved surface and the second curved surface is 0.5 mm or less, the pouch sheet is formed so that each of the inflection surfaces (126, 127) has a planar shape, and each of an angle (r) between each of the outer circumferential surfaces (124, 125) and each of the inflection surfaces (126, 127) of the pouch sheet and an angle (β) between each of the inflection surfaces (126, 127) and each of the bottom surfaces (128, 129) of the left and right accommodation grooves (121, 122) is formed at an angle of 93° to 98°, and when a length between a portion, which contacts a lower edge of the electrode assembly adjacent to the bridge in the pouch sheet, and the bridge is d1, a length between a portion, which contacts an upper edge of the electrode assembly adjacent to the bridge in the pouch sheet, and the bridge is d2, a length of the bridge is d3, a height of the electrode assembly seated on the pouch sheet is h, and a protruding height of the bridge with respect to the bottom surfaces (128, 129) of the pouch sheet is a, the pouch sheet is formed to satisfy following conditional expressions: h ≤ d1+d2+d3 and h/2 ≥ a. a forming step of pressing a pouch sheet by using a press die so that left and right accommodation grooves (121, 122), which are bilaterally symmetrical to each other and are opened upward, and a bridge connecting the left and right accommodation grooves (121, 122) to each other are formed in the pouch sheet to form a pouch sheet so that an electrode assembly is accommodated; and a folding step of seating the electrode assembly on one of the left and right accommodation grooves (121, 122) to fold the electrode assembly so that the left and right accommodation grooves (121, 122) face each other, wherein, in the forming step, the pouch sheet is formed so that the bridge protrudes upward with respect to bottom surfaces (128, 129) of the left and right accommodation grooves, and a curved portion having a rounded shape is formed on an upper end of the bridge, characterized in that in the forming step, a first bending part having a shape in which outer side surfaces of the left and right accommodation grooves (121, 122) are respectively bent downward with respect to outer circumferential surfaces (124, 125) of the pouch sheet is formed with a first curved surface having a rounded shape, a second bending part having a shape in which the outer side surfaces of the left and right accommodation grooves (121, 122) are respectively bent upward with respect to the bottom surfaces (128, 129) of the left and right accommodation grooves is formed with a second curved surface having a rounded shape, and the pouch sheet is formed so that a clearance (c) of each of inflection surfaces (126, 127) formed between the first curved surface and the second curved surface is 0.5 mm or less, the pouch sheet is formed so that each of the inflection surfaces (126, 127) has a planar shape, and each of an angle (r) between each of the outer circumferential surfaces (124, 125) and each of the inflection surfaces (126, 127) of the pouch sheet and an angle (β) between each of the inflection surfaces (126, 127) and each of the bottom surfaces (128, 129) of the left and right accommodation grooves (121, 122) is formed at an angle of 93° to 98°, and when a length between a portion, which contacts a lower edge of the electrode assembly adjacent to the bridge in the pouch sheet, and the bridge is d1, a length between a portion, which contacts an upper edge of the electrode assembly adjacent to the bridge in the pouch sheet, and the bridge is d2, a length of the bridge is d3, a height of the electrode assembly seated on the pouch sheet is h, and a protruding height of the bridge with respect to the bottom surfaces (128, 129) of the pouch sheet is a, the pouch sheet is formed to satisfy following conditional expressions: h ≤ d1+d2+d3 and h/2 ≥ a.