The invention discloses a vertical rod reinforcement device used for earth excavation and a vertical rod reinforcement method. The vertical rod reinforcement device comprises two reinforcement pieces (2) arranged on two opposite sides of a vertical rod to be reinforced (1), two supporting pieces (4) arranged on other two sides of the vertical rod to be reinforced (1), a hoisting mechanism (5) and a supporting table (6) which is connected with the vertical rod to be reinforced (1) and is used for supporting and fixing the vertical rod to be reinforced (1), wherein the upper end of the hoisting mechanism (5) is connected with the supporting pieces (4) and/or the reinforcement pieces (2), and the lower end of the hoisting mechanism (5) is connected with the vertical rod to be reinforced (1); the hoisting mechanism (5) is used for preventing the vertical rod to be reinforced (1) from sinking down. The vertical rod reinforcement device is simpler in structure, convenient to construct and stable and firm in effect and can guarantee the safety in an earth excavation process.