For the actual demand of analyzing intraseasonal oscillation of atmospheric heat source over the Tibetan Plateau,this paper devises Lanczos filter suitable for filtering quasi-two-week(10—20 d) and quasi-one-month(20—40 d) oscillations.By using the quantitative analysis and comparing with the filtering effect of Butterworth filter,the critical values l₀ of window width parameter l of quasi-two week and quasi-one month Lanczos filter are determined as 24 and 46,respectively.The filtering capability of Lanczos filter is better than that of Butterworth filter when l is greater than or equal to l₀.The whole atmospheric heat source data of the grid point(30°N,90°E) near Lhasa from 1950 to 2006 are used for test.Results indicate that,filtered by Lanczos filter with its parameter l being equal to 121,the quasi-two week and the quasi-one month components are dependable and can be used to analyze interannual difference and intraseasonal process of intraseasonal oscillation intensity of atmospheric heat source over the Tibetan Plateau.