The invention provides an open-loop control method for the rotation speed change of reaction wheels (hereinafter referred to as flywheels) and an unloading method. The open-loop control method for the rotation speed change of the reaction wheels and the unloading method comprise the following specific steps that 1, controlling is conducted through the four flywheels, and the instruction of the magnitude of the reaction wheel control torque of the fourth flywheel is adjusted to be consistent with the magnitude of the theoretical nominal rotation speed friction torque; 2, a control instruction output by a controller is limited within the maximum output torque, the control torque of each flywheel is distributed according to a flywheel distribution matrix, after the control torque of each flywheel is distributed, the flywheel with the maximum output torque is limited within the maximum torque, and the control torque of the other two flywheels is decreased and increased proportionally; 3, the momentum of a synthetic angle of the four flywheels is calculated, and when any axial angle momentum reaches the unloading threshold range and the relationship between the magnetic field intensity and an angular momentum included angle during unloading is met, magnetic torquers are started to be uninstalled; and 4, the magnetic torquer with the maximum unloading capacity is selected to work, and the flywheels are unloaded by adopting a switch control mode.