Aiming at the problem of underdetermined blind separation of attenuated and delayed mixing communication signal, this paper proposed an algorithm based on shortest distance to estimate original signals, calculating the shortest distance from mixing signal vector to subspace spanned of mixture vector firstly. Then it estimated the number of active original signal simultaneously, translated the problem of underdetermined mixture into over-determined mixture, and completed the estimation of original signal by solving the over-determined equation. The efficiency of the algorithm is proved in theory. Computer simulations show that the proposed recognition algorithm is high in performance.