The method for estimation of the parameters of the residence time distribution (RTD) of gas stream elements in cylindrical apparatus packed with granular bed has been improved. The method is based on mathematical interpretation of the function approximating the variations of the "tracer" instantaneous concentration in the gas leaving the bed (the system output signal) under assumption that the tracer instantaneous concentration in the gas entering the bed (the system input signal) is the ideal delta-Dirac impulse, as well as that the output signal of the bed is not deformed by the detector monitoring the instantaneous tracer concentration at the outlet of the bed. The improvement of the method consists in experimental determination of the function approximating the real input signal, comprising the detector effect, and in using it on the basis of the functions convolution theorem in mathematical interpretation of the function approximating the recorded output signal of the bed. Considerable differences have been found between the values of the RTD parameters, e.g. the modal time and the axial dispersion coefficient, estimated by the actually accepted method and by the method improved. It seems that the method improved can be applied for precise estimation of the RTD parameters in any flow system.