A modified lock-in notch filter (MLINF), based on an injection synchronized solid-state microwave (SSMW) oscillator and a voltage-controlled microwave phase shifter (VCMPS) has been proposed. The improved strong-signal rejection capability of the MLINF and the better weak signal amplifying property of the system, based on MLINF have been observed through analytical studies. The algorithm of the MLINF has been experimentally tested in the RF band.