In recent years, with the rapid development of fiber manufacturing technology and femtosecond laser technology, the femtosecond optical frequency combs (FOFCs) technology represented by Er-FOFCs has gradually advanced the field of optical frequency measurement. It is playing an increasingly important role in length measurement, precision spectral analysis, ultra-low phase noise microwave frequency generation, precision time-frequency transfer, temperature measurement, and many other fields. It has become an important fundamental tool in high-end scientific research. However, the important problem to be solved by the FOFCs is to measure the optical frequency. This article mainly focuses on the demand for measuring optical frequency parameters. An optical frequency comb based on the Er-doped fiber femtosecond laser has been developed. With the stable operation of the Er-FOFC, the nonlinear optical frequency conversion is used to transfer the spectrum from the central wavelength of the Er-FOFC to other wavelengths. The beat note between the broadened spectrum in the Er-FOFC and the measured laser is detected. The Er-FOFC has a spectral range of 500 ~ 2 000 nm, frequency instability and accuracy of the level of 10 -16 , and a Hz-level comb tooth linewidth. These parameters meet the requirement for measuring laser frequency. The reported Er-FOFC provides a fundamental measurement tool for optical frequency, frequency drift, frequency linewidth, and other parameters.