In hollow cathode discharge laser induced fluorescence experiment,when a strong external magnetic field is applied in the direction of observation and “magic angle” excitation method is adopted,to ArI5p[3/2]2,we find that the stronger the magnetic field,the faster the collision depopulation rates,but the slower the collision disalignment rates.On the whole,the decay rates of the curves become slower with the increase of the magnetic field strength.The natural lifetime of ArI5p[3/2]2 was measured to be 120±5ns under the condition without an external magnetic field.