The real triggered single molecule source is recognized as an ideal single photon source with a Poissonian statistics background. By considering the effect of the triplet state in single molecule energy level, an explicit function is given for the signaltobackgound ratio(SBR) by use of photoncounting statistics. When PRS(1)2PRS(2)-3PRS(2), we present an effici ent method to determine the SBR of the triggered single photons source, which s hows SBR=P2RS(1)/2PRS(2).In addition, the expression of Q, as a function of signaltobackgound ratio, has been obtained. It turns o ut that this method is simpler and gives a greater accuracy than previous proce dures.