Fully　Homomorphic　Encryption　(FHE)　is　a　key　technology　enabling　privacy-preserving　computing.　However,　the　fundamental　challenge　of　FHE　is　its　inefficiency,　due　primarily　to　the　underlying　polynomial　computations　with　high　computation　complexity　and　extremely　time-consuming　ciphertext　maintenance　operations.　To　tackle　this　challenge,　various　FHE　accelerators　have　recently　been　proposed　by　both　research　and　industrial　communities.　This　article　takes　the　first　initiative　to　conduct　a　systematic　study　on　the　14　FHE　accelerators:　cuHE/cuFHE,　nuFHE,　HEAT,　HEAX,　HEXL,　HEXL-FPGA,　100x,　F1,　CraterLake,　BTS,　ARK,　Poseidon,　FAB,　and　TensorFHE.　We　first　make　our　observations　on　the　evolution　trajectory　of　these　existing　FHE　accelerators　to　establish　a　qualitative　connection　between　them.　Then,　we　perform　testbed　evaluations　of　representative　open-source　FHE　accelerators　to　provide　a　quantitative　comparison　on　them.　Finally,　with　the　insights　learned　from　both　qualitative　and　quantitative　studies,　we　discuss　potential　directions　to　inform　the　future　design　and　implementation　for　FHE　accelerators.