The invention provides a method and a device for estimating the transient stability limit of a power transmission channel, which belong to the field of power systems. The method and the device for estimating the transient stability limit of a power transmission channel provided by the invention are applied to a power system. The power system includes a generator and a power transmission channel. The method includes the following steps: obtaining the static stability limit power of the power transmission channel before and after fault; calculating the power angle of the generator at the momentof fault removal according to the static stability limit power of the power transmission channel before and after fault; after the generator at the moment of fault removal is obtained, calculating a coefficient K according to the power angle of the generator at the moment of fault removal; and after the coefficient K is obtained, calculating the transient stability limit power of the power transmission channel according to the static stability limit power of the power transmission channel after fault and the coefficient K. There is no need to regulate the voltage and reactive power repeatedly,and the calculation efficiency is greatly improved.