In this paper starting with the general expression of the reverberation intensity for short pulses Ir(t,τ)=Kτt-me-βt, the corresponding exact expressions of the reverberation intensity for longer pulses are derived. The corresponding approximate formulae are also presented under the assumption that the exponential attenuation loss over the pulselength can be neglected. It is shown that, at short ranges, the reverberation intensity tends to saturation and decays inversely with the (m-l)st-power of the time t when the exponential attenuation coefficient β is small enough and the pulselength τ longer than the effective pulselength τm=amt(am decreases as m increases, and m is a real number greater than 2). Experimental results agree well with the theory.