The following new ideas are presented for use in on-line fault diagnosis of analog integrated circuits.1. The number of fault elements in an analog circuit can be evaluated from the measured data upon the limited number of accessible terminals.2. The dependent relation between any two multiple-fault sets can be classified in two kinds: the mutual dependence and the single dependence. The routine of on-line fault diagnosis can be accelerated with the use of mutual dependence.3. The idea of effective measuring ports is helpful to the topological judgement of diag-nosability of certain multiple-fault set besides the examination of the existence of loops and cutsets among the fault elements.4. The uniqueness of the values of certain existing fault elements calculated from the measured data upon the different measuring ports can be used to distinguish the actual fault from the guessed fault.Program based on the algorithm derived from the above ideas has been proved with success.