To reduce the threshold is an important requirement for utilizing the random laser. RFL (random fiber laser) is a new random laser which user the photonic bandgap of PCF to lower the threshold by filling the random medium into a hollow-core PCF. Theoretical analysis shows that most of the emitted light is concentrated in the core of the fiber because of the controlling of the bandgap, which should enhance the interaction between the random medium and the localized light for the light oscillating back and for the thin core region, therefore the excitation efficiency of the random laser could be improved. However, the band gap of PCF filled with the random medium should be changed, so when choosing fiber to reduce the threshold for RFL, we should consider the matching between the new bandgap of the padded fiber and the gain frequency of the medium, and arrange the fiber and medium in pairs reasonably. If the PCF matches with the medium, the lasing may be enhancedly regulated and controlled and the threshold can be reduced greatly.