The invention discloses a tension adjusting device and method for steel wire ropes on a hoisting container of an ultra-deep vertical shaft. The tension adjusting device comprises two stages of steel wire rope tension adjusting devices arranged on the hoisting container, wherein the first-stage steel wire rope tension adjusting device comprises a left steel wire rope tension adjusting device and a right steel wire rope tension adjusting device which are arranged in symmetry; the second-stage steel wire rope tension adjusting device is arranged below the first-stage steel wire rope tension adjusting device; through the two stages of steel wire rope tension adjusting devices, the tensile forces of the four steel wire ropes can be adjusted and balanced, and the requirement on tension balance in the hoisting process is met; the four steel wire ropes are divided in pairs, a first-stage winding drum on which two of the four steel wire ropes are wound is rotated to adjust the tensile forces of the two steel wire ropes, and meanwhile a second-stage winding drum on which the steel wire ropes are wound is further rotated to adjust the tensile forces of the four steel wire ropes, so as to achieve the final purpose. The tension adjusting device is simple in structure, convenient to mount and easy to disassemble; besides, the tensile forces are adjusted automatically by rotating the winding drums, and therefore the method is novel and wide in the range of application.