Using infrared to (sub)millimeter data from Spitzer, Herschel, the James Clerk Maxwell Telescope, and the IRAM 30m telescope, we conducted an unbiased survey of the massive dense cores (MDCs) in the Cygnus X molecular cloud complex, aimed at characterizing the physical conditions of high-mass star formation (HMSF) at ~0.1pc scales. We created 5{deg}x6{deg} images of the 70-1200{mu}m dust continuum, gas column density, and dust temperature of Cygnus X. A spatial relation between the dense regions (A_v_>=15) and the developed HII regions was found, indicating the impact of the latter on the global structures of Cygnus X. With a 35M_{sun}_ mass threshold implied by HMSF signposts, we identified 151 MDCs with sizes of ~0.1pc, masses of 35-1762M_{sun}_, and temperatures of 8-35K. Our MDC sample is statistically complete in Cygnus X and is three times larger than that in Motte+ (2007, J/A+A/476/1243). The MDCs were classified into IR-bright/IR-quiet ones based on their midinfrared fluxes, and a large "IR-quiet" proportion (90%) was found in our sample. Two possible scenarios were proposed to interpret accelerated HMSF and the incapability of HMSF of the IR-quiet MDCs. We also found 26 starless MDCs by their lack of compact emissions at 21-70{mu}m wavelengths, of which the most massive ones are probably the best candidates of initial HMSF sites in Cygnus X.