Abstract: A transmission power testing bar of a cable television system is coupled to the test hole of a main line distributor and provided with an inner sleeve having therein a test set member comprising a test point, an attenuation line, and an insertion hole. The inner sleeve is provided at one end thereof with a spring for providing the test set member with an elastic force enabling the test point to urge intimately the center point of the test hole of the main line distributor. The testing bar further comprises an outer sleeve and a copper connection head. The outer sleeve is fitted over the inner sleeve and the spring such that the outer sleeve can be caused to move axially. The copper connection head is fastened at one end thereof with the inner sleeve and at another end thereof with a signal gauge for measuring the transmission power value of a coaxial cable.