The experiments reveal, for the RF filter, the out-off-band transfer property under ultra wide band (UWB) pulses is essentially in agreement with that of continous wave (CW). However, for some frequencies in the in-band of the filter, the transfer function of UWB is much larger than 1. Moreover, the oscillating property is found in the time domain response of the filter. Therefore, based on the nonlinear passive intermodulation (PIM) and the Q-value, the response mechanisms of the filter are studied. The PIM of the filter shows nonlinear effects under the two different field strengths, which results in the limited universality of measurement results. Furthermore, the signal through the filter is predicted by making use of the two measured transfer functions. The predicting results under CW pulse are smaller than the measured ones in energy and peak power. In a word the response mechanisms of the filter under UWB pulse does differ from the that under CW pulse, i. e., the measured results of CW can’t be applied for the UWB effect analysis and evaluation.