Provided are a method for transmitting an uplink signal, a terminal device and a network side device. The method comprises the steps that a terminal device receives first information sent by a networkside device, the first information being used for the terminal device to determine a beam or beam group used for sending an uplink signal to the network side device; according to the first information, the terminal device determines a target beam or target beam group for sending the uplink signal; the terminal device uses the target beam or target beam group to send the uplink signal to the network side device. The present invention improves the uplink signal reception performance of the network side device.