A voltage balance control device (1a, 1b, 1c) for a flying-capacitor multilevel converter, the flying-capacitor multilevel converter including plural flying capacitors (C 1 to C p), even-numbered switch elements (Q 1 to Q p and Q 1b to Q pb) and a filtering inductor (L f), the even-numbered switch elements (Q 1 to Q p and Q 1b to Q pb) being serially connected between a positive electrode and a negative electrode of a DC voltage source, the filtering inductor (L f) being connected with a middle point of the serially-connected even-numbered switch elements (Q 1 to Q p and Q 1b to Q pb), a first end of each flying capacitor (C 1 to C p) being connected with two adjacent switching elements (Q 1 to Q p and Q 1b to Q pb) at a first side of the middle point, a second end of each flying capacitor (C 1 to C p) being connected with two adjacent switching elements (Q 1 to Q p and Q 1b to Q pb) at a second side of the middle point, the even-numbered switch elements (Q 1 to Q p and Q 1b to Q pb) being operated at the same switching period, the voltage balance control device (1a, 1b, 1c) comprising: a control signal processor configured to generate plural control signals corresponding to the switch elements (Q 1 to Q p and Q 1b to Q pb), thereby controlling on/off states of the switch elements (Q 1 to Q p and Q 1b to Q pb); characterized in that a voltage/current detecting unit is configured to detect voltage values (V c1 ∼V c(p-1)) of the plural flying capacitors (C 1 to C p-1) to output a first detecting result (X a), and configured to detect an operating status of the flying-capacitor multilevel converter to output a second detecting result; a capacitor voltage balance controller is configured to receive the first detecting result (X a) and configured to generate plural first duty cycle differences (ΔD 10 ∼ΔD (p-1)0) according to a result of comparing the voltage values (V c1 ∼V c(p-1)) of the first detecting result (X a) with plural anticipated voltage values (V c1 *∼V c(p-1) *) of the plural flying capacitors (C 1 to C p-1); a current direction forecasting unit is configured to calculate a current direction adjusting signal (Sign) in each adjusting period according to the voltage value (V cm) of any selected flying capacitor (C m) from the first detecting result (X a) and a feedback signal, wherein the feedback signal is related to the duty cycle difference between the duty cycles (D m and D m+1) of the two serially-connected switch elements (Q m and Q m+1) corresponding to the selected flying capacitor (C m), and the adjusting period is an integer multiple of the switching period; and a computing unit is configured to perform multiplication and/or division on the current direction adjusting signal (Sign) and the plural first duty cycle differences (ΔD 10 ∼ΔD (p-1)0), thereby generating corresponding second duty cycle differences (ΔD 1 ∼ΔD (p-1)), wherein the control signal processor is configured to generate the plural control signals according to a reference value (X Ref *), the second detecting result and the plural second duty cycle differences (ΔD 1 ∼ΔD (p-1)), wherein the voltage values (V c1 ∼V c(p-1)) of the plural flying capacitors (C 1 to C p-1) are maintained at the corresponding anticipated voltage values (V c1 *∼V c(p-1) *) according to the plural duty cycle signals (D 1 to D p). a control signal processor configured to generate plural control signals corresponding to the switch elements (Q 1 to Q p and Q 1b to Q pb), thereby controlling on/off states of the switch elements (Q 1 to Q p and Q 1b to Q pb); characterized in that a voltage/current detecting unit is configured to detect voltage values (V c1 ∼V c(p-1)) of the plural flying capacitors (C 1 to C p-1) to output a first detecting result (X a), and configured to detect an operating status of the flying-capacitor multilevel converter to output a second detecting result; a capacitor voltage balance controller is configured to receive the first detecting result (X a) and configured to generate plural first duty cycle differences (ΔD 10 ∼ΔD (p-1)0) according to a result of comparing the voltage values (V c1 ∼V c(p-1)) of the first detecting result (X a) with plural anticipated voltage values (V c1 *∼V c(p-1) *) of the plural flying capacitors (C 1 to C p-1); a current direction forecasting unit is configured to calculate a current direction adjusting signal (Sign) in each adjusting period according to the voltage value (V cm) of any selected flying capacitor (C m) from the first detecting result (X a) and a feedback signal, wherein the feedback signal is related to the duty cycle difference between the duty cycles (D m and D m+1) of the two serially-connected switch elements (Q m and Q m+1) corresponding to the selected flying capacitor (C m), and the adjusting period is an integer multiple of the switching period; and a computing unit is configured to perform multiplication and/or division on the current direction adjusting signal (Sign) and the plural first duty cycle differences (ΔD 10 ∼ΔD (p-1)0), thereby generating corresponding second duty cycle differences (ΔD 1 ∼ΔD (p-1)), wherein the control signal processor is configured to generate the plural control signals according to a reference value (X Ref *), the second detecting result and the plural second duty cycle differences (ΔD 1 ∼ΔD (p-1)), wherein the voltage values (V c1 ∼V c(p-1)) of the plural flying capacitors (C 1 to C p-1) are maintained at the corresponding anticipated voltage values (V c1 *∼V c(p-1) *) according to the plural duty cycle signals (D 1 to D p).