Instantaneous frequency measurement (IFM) is one of great important technologies in modern electronic warfare. The photon-assisted IFM technology was paid particular attentions due to its huge bandwidth, low loss, small size, light weight, as well as electromagnetic inference immunity, which can overcome the bottleneck of traditional electronic methods. Based on the existing research, another photon-assisted instantaneous frequency measurement method with smaller frequency measurement error was put forward, which realized the frequency measurement of 0.5~18.5GHz signals by constructing an optical link with complementary characteristics of radio frequency power response. The results show that the signal gain is consistent with that of theory. Then the amplitude comparison function with more steep slope, is derived to measure the unknown signal frequency, which can improve its accuracy. The experimental results indicate that the frequency measurement error is less than 30MHz. Moreover, this method is very simple and just a few ordinary optical devices are needed. Meanwhile, it has favorable ability to adapt to the environment. By replacing the modulator and photodetector with that of higher operation frequency, it can be easily extended to work for ultra-wide band signal measurement.