The invention discloses a real-time on-line detecting apparatus of smoke pollutant and the test method thereof, and relates to the atmospheric environmental monitoring. The apparatus comprises a pulse generator (1), a pulse laser (2), a time delayer (3), a reflector (4), a long-focus focusing lens (5), a light receiving device (6), optical fibre (7), a spectrometer (8), an A/D converter (10), and a computer (11). The invention utilizes a focused high energy laser beam to motivate the substance in the smoke gas to be the high energy state, various substances radiate respective characteristic spectrums during the process of the high energy state returning the base state, the composition of the pollutant such as magnesium, iron, copper, aluminum, lead, chrome, hydrargyrum, arsenic, etc. in the tested smoke gas and the concentration thereof can be obtained by analyzing the characteristic spectrums. The invention has the advantages of simple structure, reliable method and convenient operation, and is suitable for performing the real-time and on-line continuous detection of the pipeline smoke gas during the combustion process of coal.