The crosstalk phenomenon and its influence in the determination of gross α and β radioactivity when using a low background gas-flow proportional counter as a measuring instrument was examined in this paper. The crosstalk ratio between α and β channel was measured by using a series of α, β metal planar sources, powder sources, and thin-layer surface sources. The β-to-α crosstalk ratio of ⁹⁰Sr-⁹⁰Y metal planar sources and powder sources containing ¹⁴C, ¹³⁷Cs, ⁹⁰Sr-⁹⁰Y, or ⁴⁰K is less than 0.1%, which can be negligible. The crosstalk ratios of α metal planar source in ascending order are ²¹⁰Po, ²⁰⁹Po, ²³⁹Pu, ²³⁹Pu-²⁴¹Am mixed source, and ²⁴¹Am, which range from 3.49% to 25.4%. The crosstalk ratio of ²⁴¹Am is significantly higher than those of other sources. Furthermore, ²⁴¹Am powder sources' crosstalk ratio increases with mass thickness. The crosstalk of α particles to β channel is obvious and related to the sample source preparation method. This is mainly due to the difference in self-absorption due to different source preparation methods. Overall, the crosstalk ratio of α powder sources is larger than thin-layer surface sources and metal planar sources. The interference of α-to-β crosstalk should be considered. By covering the sample sources with aluminum foil or paper with a certain thickness, the crosstalk interference of α-to-β can be reduced effectively. Additionally, it is an effective way to directly correct the count rate by the crosstalk ratio. In this case, it is necessary to consider the consistency of the sample source to be measured and the crosstalk ratio scale source, as any discrepancies can lead to a significant deviation in the corrected result.