Abstract: The Global Navigation Satellite System Reflectometry (GNSS-R) is a new ocean remote sensing technique using L-band forward quasi-specular scattering navigation signals. After comparing the similarities and differences between GNSS-R and other microwave remote sensing techniques, two methods of retrieving Significant Wave Height (SWH) by GNSS-R are proposed: one is a direct method using the leading edge slope of the normalized delay waveform; the other is indirect based on the sea surface roughness measurement. The feasibility and sensitivity of the two methods are analyzed through theoretical model and actual measurements from Fengyun-3E data. The results show that due to the low ranging accuracy from GNSS signals bandwidth, the leading edge slope is almost insensitive to SWH, which cannot be used for retrieval; the sea surface roughness from GNSS-R can be used to retrieve SWH with an accuracy of about 0.5～0.55 m. Although it still has some limitations, it can be used as a good supplementary means to obtain SWH data. The results of this paper can also provide guidance for the design of future GNSS-R satellite missions.