A tunable, narrow bandwidth, negative coefficient microwave photonic filter based on cascaded dispersion devices was proposed, because the negative coefficient microwave photonic filter was very difficult to realize by the way of positive coefficient optical taps. The reshaped output signals of the multi-wavelength fiber laser were used as the tap of the filter. SMF and the F-P fiber ring were cascaded as a delay unit to realize the frequency selectivity of the filter. The negative coefficient was realized by a mixture of phase modulator and cascaded dispersion devices. As many as 37 stable laser signals with 0.34 nm wavelength interval were obtained by the experiment. And then based on the experiment results, the effects of coupling coefficient r of C2, C3 in the F-P fiber ring, different length TODL, and different length SMF in the delay unit etc. on the microwave photonic filters performance were simulated and studied.