There are provided a method for analyzing an aqueous ammonium carbamate solution Whereby the composition of an unreacted-gas absorber outlet liquid can be specified in real time, and a method for operating an unreacted gas absorber by use of the same. The method for analyzing the composition of an aqueous ammonium carbamate solution includes determining ammonia component concentration, carbon dioxide component concentration, and Water concentration of the aqueous ammonium carbamate solution, Which is the unreacted-gas absorber outlet liquid in a urea production process, by using a correlation among viscosity, temperature, and carbon dioxide component concentration of the aqueous solution and a correlation among density, temperature, ammonia component concentration, and carbon dioxide component concentration of the aqueous solution, Wherein the ammonia component concentration is a concentration of a sum of free ammonia and equivalent ammonia of ammonium carbamate Which are contained in the aqueous solution, and the carbon dioxide component concentration is a concentration of equivalent carbon dioxide of ammonium carbamate contained in the aqueous solution.