The invention provides a method for ammonia-process capture of carbon in flue gas and synthesis of chemical products. The method is implemented in a flue gas absorption and synthesis apparatus. The flue gas absorption and synthesis apparatus comprises a flue gas pipeline, an absorbing tower and a carbonization tower which are in parallel connection, an ammonia removing tower and a solid-liquid separating unit. The method comprises the following steps: absorption and removal of CO2; carbonization for output of sodium bicarbonate; washing of flue gas for recovery of ammonia; solid-liquid separation; etc. According to the method, the absorbing tower and the carbonization tower are parallely connected to shunt flue gas at the same time, ammonia water is used as an absorbent to capture CO2 in the flue gas, and sodium sulfate is used as a conversion medium to produce chemical products like sodium carbonate and sodium bicarbonate. With the method, product crystallization and carbon dioxide absorption are carried out at the same time; the carbonization degree of mother liquor is increased while carbon emission is further reduced; and decarburization efficiency and product yield are improved. Industrial application of the method can be realized.