The invention discloses an electric height adjusting device for a seat. The electric height adjusting device comprises a seat height adjusting toothed plate and an electric mechanism driving the seat height adjusting toothed plate to rotate. The electric mechanism comprises a reduction gearbox body, a motor, a worm, a
bevel gear component, a flexible bearing, a flexible wheel, a rigid wheel body, a reduction gearbox cover and an output transmission piece. The direct-current motor is used as a power source of the electric mechanism,
motor torque is transmitted to the worm and then transmitted to the
bevel gear component through the worm, and first-level
speed reduction of the electric mechanism is composed of the worm and the
bevel gear component. After first-level
speed reduction transmission is completed, power is output to the output transmission piece through a
harmonic gear mechanism composed of the bevel gear component, the flexible bearing, the flexible wheel to be output. The electric height adjusting device for the seat has the advantages of being small in size, large in output torque, large in
transmission ratio, high in transmission precision, small in return
stroke clearance, high in
bearing capacity and the like, adjustment handleability and the overall strength of the seat are increased, and the
noise level is greatly lowered.