All-optical 3R (reampifying, retiming, reshaping) technique is the trend of the all-optical communication network and all-optical clock recovery is one of the key techniques of all-optical 3R technique. With the application of new phase modulation format, the research of all-optical clock recovery of new phase modulation format is attracting more and more attention. A new scheme of clock recovery of variable bit-rate non-return-to-zero differential phase shift keying (NRZ-DPSK) signal based on tunable demodulator is proposed. The tunable demodulator composed by Fizeau interferometer based on free space light converts the NRZ-DPSK signal into return-to-zero (RZ) signal which includes clock component. The demodulator can demodulate 2.5 Gb/s to 40 Gb/s NRZ-DSPK signal. The demodulated RZ signal is injected into the fiber loop laser and all-optical clock recovery from the length of 27-1 pseudo-random bit sequence (PRBS) NRZ-DPSK signal is realized. The extinction rate of the recovered clock is higher than 10 dB.