Microwave photonic filter (MPF) as one of the key devices in the radio-on-fiber (ROF) system has attracted much interest recently. Some key technologies of MPF including the coherence, quality factor (Q) and reconfigurability are introduced. The difference between the incoherent and coherent MPF (ICMPF and CMPF) is given, and the methods to realize an ICMPF are also introduced. Higher Q factor MPF can be developed with more taps, and it is proved by simulation. Then the methods of finite and infinite impulse response MPF (FIRMPF and IIRMPF) are both given. At last, the reconfigurability is verified by four kinds of window functions.