Secondary soil salinization is a common problem in intense agroecosystems such as the plastic shed production (PSP) systems. Understanding the dynamic changes of soil salinity and its negative impacts on crop nutrition is essential for management of PSP systems. In this study, 96 plastic shed orchards were chosen to investigate the impact of long-term PSP on soil salinization in a perennial fruit production county in Shaanxi Province, West China. The following results were obtained by comprehensively analyzing the profile distribution, spatiotemporal distribution, and the composition of soil salinity in PSP systems. Compared with the cereal and natural soil, PSP soil had significantly higher soil nutrients in addition to lower soil pH and greater soil electrical conductivity (EC) values. Soil EC had significant positive correlations with the total soluble salt (TSS) and sodium adsorption ratio in PSP soil profiles (p < 0.01). Thus, the high EC value (1082.2 ± 1200 μS cm⁻¹) of PSP soil indicated high soil salinity content and Na⁺ concentration in the soil solution in the study area. The average content of TSSs in the topsoil of the soil profiles in PSP systems reached 2.23 g kg⁻¹, indicating moderate salinization (2 g kg⁻¹ ≤ TSS < 4 g kg⁻¹). Furthermore, soil EC had a positive correlation with the PSP cropping duration and a negative correlation with the Ca concentration in fruit tree leaves in PSP systems. These findings suggest that increasing soil salinity might suppress the nutrient uptake by PSP fruit trees. Overall, this study concludes that high inputs of agrochemicals, high evaporation, and minimal leaching in PSP systems significantly intensify secondary soil salinization, as well as high Na⁺ accumulation in surface soil, which threaten the growth of fruit trees and soil functions.