Effect factors of the absorption of the source,air,entrance window,and dead layer of a detector must be considered in the measurement of monoenergetic alpha particles,along with statistical noise and other factors that collectively cause the alpha spectrum to exhibit a well-known low-energy tail.Therefore,the estabUshment of an alpha spectrum detector response function from the perspective of a signaling system must consider the various factors mentioned above.The detector response function is the convolution of an alphaparticle pulse function,two exponential functions,and a Gaussian function,followed by calculation of the parameters of the detector response function using the weighted leastsquares fitting method as proposed in this paper.In our experiment,~(239)Pu alpha spectra were measured by a highresolution,passivated implanted planar silicon(PIPS)detector at 10 levels of vacuum and 10 source-detector distances.The spectrum-fitting results were excellent as evaluated by reduced Chi-square(x~2) and correlation coefficients.Finally,the variation of parameters with vacuum level and source-detector distance was studied.Results demonstrate that σ,τ_1,and τ_2 exhibit no obvious trend of variation with vacuum in the range 2000-20,000 mTorr,and at a confidence level of 95%,the values of τ_1 and τ_2 decline in a similar fashion with source-detector distance by the power exponential function,while the value of a declines linearly. Effect factors of the absorption of the source, air, entrance window, and dead layer of a detector must be considered in the measurement of monoenergetic alpha particles, along with statistical noise and other factors that collectively cause the alpha spectrum to exhibit a well-known low-energy tail. wherefore, the estabUshment of an alpha spectrum detector response function from the perspective of a signaling system must consider various factors mentioned above the detector response function is the convolution of an alphaparticle pulse function, two exponential functions, and a Gaussian function, followed by calculation of the parameters of the detector response function using the weighted least squares fitting method as proposed in this paper. Our experiment, ~ (239) Pu alpha spectra were measured by a high resolution, passivated implanted planar silicon (PIPS) detector at 10 levels of vacuum and 10 source-detector distances.The spectrum-fitting results were excellent as evaluated by reduced Ch i-square (x ~ 2) and correlation coefficients. Finally, the variation of parameters with vacuum level and source-detector distance was studied. Results demonstrated that σ, τ_1, and τ_2 exhibit no obvious trend of variation with vacuum in the range 2000 -20,000 mTorr, and at a confidence level of 95%, the values ​​of τ_1 and τ_2 decline in a similar fashion with source-detector distance by the power exponential function, while the value of a declines linearly.