Abstract: This article reviews the commonly used methods for expression of radar's ECCM performance, points out their disadvantages and proposes that it is required to establish the formulae which consist only of the radar's technical parameters in order to measure the radar's ECCM capabilities.By means of logical argumentation and ambiguity function theory we can derive the followings: （ 1 ） The radar's 4-dimensional generalized resolution parameter can be used to express the radar's basis anti-clutter capability. The simplified expression of this parameter is T0 （the dwelling time at a radar's target, or the integration time of a echo signal of the radar） × Bs （the radar signal bandwidth） X G （the radar antenna gain）; （ 2 ） The product of an average radar's transmitting power and its generalized resolution parameter PT0×BsG can be used to express the radar's anti-jamming capability, and the same formula may also be used to express the total interference rejection capability in gross.By another approach, I. e. by calculation of the radar's output signal to interference power ratio under various interference conditions, the given formulae have further been proven. The given formulae consisting of the radar's fundamental parameters are the fundamental parts of the measuring formula of the radar's ECCM capabilities. They represent the radar basic or potential ECCM performance. The supplementary factors for the ECCM capability formulae are composed of the technical specifications of the radar's ECCM devices. The general rule of com-position is to take the typical quality level （or the middle level） specification （in db） as the base figure. If the quality level of some devices is higher,a positive factor will be got, and if lower-a negative. For example, theequation for MTI supplementary factor ρM isρM（db） = SCV-25（db） where 25 db is the middle level specification for SCV of modern MTI radar.As many radar systems consist of multiple channels, in this article we propose a set of equations for the multichannel radar system's ECCM capabilities in terms of the ECCM capabilities of the individual channel.In the last part of this article, 4 radar systems are taken as examples, their ECCM capabilities are calculated by means of the given formulae. Application of obtained results to radar's system analysis and system design are discussed.