In this paper, we propose a method to realize microwave photonic filter (MPF) with complex coefficient, whose central frequency f0 and 3 dB bandwidth are tunable. The complex coefficient is realized by multi-wavelength optical source and stimulated Brillouin scattering (SBS). The central frequency of the filter is tuned by adjusting the phase shift caused by SBS without changing its frequency response. The frequency selectivity of filter can be improved through increasing the bandwidth of broadband optical source (BOS) or decreasing wavelength separation to increase the taps of MPF. The mainlobeto- sidelobe suppression ratio (MSSR) of the filter is affected by the weight of each tap. When the length of fiber is 0.5544 m in birefringence fiber loop mirror (FLM), the MSSR is improved by 18.55 dB compared with that without the weight controlling.