The stochastic resonance (SR) in a time-delayed mono-stable system driven by multiplicative white noise, additive white noise, additive dichotomous noise as well as a periodic square-wave signal is considered from the view of the signal-to-noise ratio (SNR).It is found that the SNR increases monotonically with the increase of the delay time.The SNR exhibits the SR behavior when it is plotted as a function of intensities of the noises, displaying the asymmetry of the dichotomous noise.The SNR varies non-monotonically with the increase of the system parameter and the amplitude of the input square-wave signal.