Microwave photonic-assisted instantaneous frequency measurement (IFM) system has many advantages such as high time-bandwidth product, low power consumption, light weight and anti-electromagnetic interference. Domestic and foreign IFM systems are introduced respectively according to three kinds of mapping modes such as frequency-space, frequency-time and frequency-amplitude. And IFM system with frequency-amplitude mapping relationship is mainly concluded and compared. According to the trade-off problem between measurement range and accuracy, IFM researching technology with high accuracy and tunable measurement range is further presented. And the current researches in the fields are reported.