The multipath fading independency between different Global Navigation Satellite Systems（GNSS） frequency bands and space-separated antennas can be used to improve robustness of high-precision GNSS receivers in harsh urban environments. This research focuses on a new sensitive and robust fading monitoring architecture for GNSS diversity branches, and implementation of the method on an Adaptive Diversity reception-based Tracking Loop（ADTL）. Firstly, fluctuations in the amplitude and phase of multipath fading signals are characterized. Performance of different design parameters in the fading monitoring method is analyzed in details. Next, diversity combining strategies including the non-linear Selective Combining（SC） and the Maximum-Ratio Combining（MRC） are utilized in ADTL for different fading conditions. Experimental results with MonteCarlo simulation and real GNSS fading signals demonstrated that: 1) the proposed novel method can achieve robust and sensitive fading monitoring with response delay less than 20 ms; 2) Compared with traditional Phase Lock Loops（PLL）, the ADTL algorithm significantly reduced the navigation bit error rate due to halfcycle sudden-phase change caused by phase losing of lock.