Provided in the embodiments of the present invention are a communications method, a terminal device, and a network device. The method comprises: a terminal device determining a first frequency-domain resource, said first frequency-domain resource being a usable resource preconfigured to support the use of a first TTI to transmit a first physical channel in a first target time unit, and the length of time of the first TTI being equal to the length of time of the first target time unit; a terminal device determining a second frequency-domain resource, said second frequency-domain resource being determined to be used for using a second TTI to transmit a second physical channel in a second target time unit, the second TTI being not smaller than the first TTI and the second target time unit at least partially overlapping with the first target time unit; a terminal device determining a third frequency-domain resource, the third frequency-domain resource containing at least part of the frequency-domain resource of the second frequency-domain resource, and said third frequency-domain resource being a maximum usable frequency-domain resource supporting the use of a first TTI to transmit a first physical channel in a first target time unit. The embodiments of the present disclosure increase resource utilization.