Random distributed feedback fiber laser (RDF-FL) is a novel kind of light source based on distributed Rayleigh scattering and Raman amplification, which has characteristics such as simple structure, good directionality as well as long-distance transmission and shows a broad prospect in the application of optical fiber sensing and communications. However, the pump threshold is relative high just because of the weak Rayleigh scattering feedback. In this paper, two methods, half-opened cavity and ultra-long ring cavity structures, are used to reduce the threshold of the RDF-FL. On this basis, the input-output characteristics and frequency spectra of the RDF-FL are analyzed theoretically and experimentally. The results show that the first-order threshold of the RDF-FL can be reduced to 0.8 W and 1.0 W respectively. This research is helpful to further understanding the mechanism of RDF-FLs as well as the design of novel random fiber lasers.