Frequency-scanning　interferometry　(FSI)　with　an　external-cavity　diode　laser　(ECDL)　is　an　effective　technology　for　the　absolute　distance　measurement　of　a　target.　The　measurement　accuracy　of　the　FSI　system　is　directly　determined　based　on　the　phase　extraction　accuracy　of　an　interference　signal.　However,　because　the　optical　frequency　scanning　of　the　ECDL　exhibits　nonlinearity,　a　large　phase　extraction　error　is　introduced　into　the　phase　calculation　result,　which　decreases　the　measurement　accuracy.　In　this　study,　a　composite　algorithm　for　implementing　phase-accurate　demodulation　is　developed　by　combining　the　phase-generated　carrier　(PGC)　technology　and　the　Hilbert　transform　(HT)　error　compensation　principle.　In　PGC　technology,　the　demodulated　phase　contains　the　nonlinear　error　and　quadrature　phase　deviation　resulting　from　an　amplitude　ratio　that　is　not　equal　to　1,　and　non-strict　orthogonality　of　the　two　quadrature　components.　To　compensate　for　these　two　errors,　HT　is　utilized.　The　amplitude　and　phase　of　one　of　the　two　quadrature　components　are　compensated　by　using　the　analytic　signals　on　the　complex　plane,　which　ensures　that　the　two　quadrature　components　have　the　equal　amplitudes　and　strict　orthogonality.　The　effectiveness　and　stability　of　this　composite　algorithm　are　verified　by　a　series　of　simulations　and　experiments.　The　experimental　results　indicate　that　the　proposed　method　is　capable　of　maintaining　the　single-cycle　relative　error　of　phase　extraction　within　the　0.3%　limit,　thereby　improving　the　measurement　accuracy　of　the　FSI　system.