Analysis of the spatial heterogeneity of soil attributes and diagnosis of the soil stress for crops cultivated at large-scale saline-alkali farmland based on remote sensing spectral indices are important to improve the land utilization efficiency and contribute to improve economic and ecological benefits. In this study, we conducted an Unmanned Aerial Vehicle (UAV) remote sensing observation and field measurement over a typical coastal saline-alkali farmland (400 hm2) in the Yellow River Delta of Dongying City, Shandong province in China during the growing season of maize and sorghum in 2019. An eBee wing-fixed UAV platform (SenseFly, Cheseaux-Lausanne, Switzerland) equipped with a multiSPEC-4C multispectral camera (SenseFly, Cheseaux-Lausanne, Switzerland) was used to capture the spectral information of crops. Nine Vegetation Indices (VIs) were selected to characterize the growth status of crops. Among the nine VIs, MCARI, TCARI/OSAVI, and NDREI were sensitive to Leaf Chlorophyll Content (LCC); OSVAI, GNDVI, and MSR were sensitive to Above-Ground Biomass (AGB); and NDVI, EVI2, and MSRRE were sensitive to Leaf Area Index (LAI). Soil sampling (n = 195) at three layers (0~10 cm, 10~20 cm, and 20~40 cm) were implemented evenly across the study area. In total, five soil attributes were measured, including soil salinity (SALT, g/kg), pH, organic matter content (C, g/kg), total nitrogen content (N, g/kg), and available nitrogen content (SN, mg/kg). In our study, we first conducted an interpolation method using Inverse Distance Weighted (IDW) to map the spatial heterogeneity of soil attributes. Our interpolation results show that all the soil attributes showed obvious horizontal spatial heterogeneity, while pH and SALT showed remarkable vertical spatial heterogeneity. Second, we conducted the Pearson Correlation Analysis (PCA) between different soil attributes at each soil layer. The results of PCA showed that SALT and pH had a significantly negative correlation, and these two attributes were not related to SN, N, and C. While SN, N, and C had significantly positive relationships with each other. Finally, the influences of soil attributes on the growth status of maize and sorghum were assessed separately using the Recursive Feature Elimination (RFE) method along with the random forest model based on 3-fold cross validation and 100 times iteration. According to the importance values of soil attributes to VIs, the influence of soil attributes on crop growth from high to low was that SN>N, C>pH>SALT for maize, and SALT>pH>SN, N, C for sorghum. However, the dominant soil attributes that influenced crop growth were SN2 (i.e., SN at 10~20 cm soil layer) and SALT at 0~40 cm soil layer for maize and sorghum, respectively. This study proposes a 'soil-crop growth-VIs' framework for monitoring crop growth status based combining field sampling and UAV remote sensing observations, which is essential for agronomic management in saline-alkali land and contributes to the development of precision agriculture.