Recently, a new method for controlling vertical acceleration and damping convection by applying an upward magnetization force (F m ) has been developed, To evaluate this method, we numerically simulate thermal convection (Ra = 33734) in pure water (5 x 10 -6 Ω -1 m -1 ) when both an upward and radial magnetization forces act on it inside a real magnet. When -μ 2 0 H(dH/dz) of vertical magnetic field gradients is 573 T 2 /m, convection is damped and the maximum velocity decreases by about 50%. Natural convection is damped with increasing -μ 2 0 H(dH/dz) when -μ 2 0 H(dH/dz) is below the critical value, 1180 T 2 /m. At 1180 T 2 /m, the maximum velocity takes a minimum value, about 1% of the velocity without a magnetic field. Above 1180 T 2 /m, the contribution from the radial magnetic force becomes dominant. Numerical simulation is also conducted for a lowconducting fluid (29 mass% NaCI solution, 21 Ω -1 m -1 ) when -μ 2 0 H(dH/dz) = 573 T 2 /m, and the contribution from magnetization force to suppress convection is larger than that from Lorenz force.