Leaf area index (LAI) is defined as half the total leaf area per unit horizontal ground surface area. LAI is a significant attribute of forest ecosystem that controls, in part, physiological processes such as photosynthesis, transpiration, and leaf maintenance respiration, as well as physical processes including canopy water interception, evaporation, and light attenuation. There are several procedures to estimate LAI, both direct and indirect. However, the direct methods are slow and labor intensive. Although remote sensing potentially offers the opportunity to access features of ecological phenomena on a large scale, the scaling effect in retrieving LAI is a significant problem because of the heterogeneity in pixels, which can be well described using a semivariogram. In this study, we monitored LAI of ten mixed spruce-fir-deciduous stands in Wangqing Forestry Bureau, Jilin Province, by using a 10 m × 10 m grid in 1 hm² plots and digital hemispherical photography (DPH), the most commonly implemented method in forest research. In total, we obtained 1000 LAI values in these plots. The spatial heterogeneity of the LAI was explored using geostatistical analysis. We found that the average LAI in mixed spruce-fir-deciduous stands was 2.410, ranging from 1.265 to 4.029. LAI had low variability within and among plots, with the coefficient of variation ranging from 9.981% to 19.440%. Linear, hole, and Gaussian models were found to best describe the spatial autocorrelation of LAI. The coefficients of determination of these models were between 0.643 and 0.880. The LAIs had strong, moderate and weak spatial dependence according to their structure ratios. The ranges of these semivariogram models varied greatly, from 15 to 155 m, with an average of 65.637 m. One reason for the large range was the large homogeneous areas at the scale that were longer than the lags for which the semivariograms were calculated. Ordinary kriging was used to analyze the spatial distribution of LAI and showed apparent belt- and spot-shaped massive gradient changes. The relationship between LAI and stand variables was examined. LAI exhibited a significantly negative relationship with average diameter at breast height, average height, and average crown length, but showed a significantly positive relationship with average crown width, stand density, and tree species richness. LAI was closely related to tree species, and plots with few coniferous species had low values. Some unknown factors also contributed to the pattern of LAI in these plots. The results of this study provide a reference for estimating LAI at stand and large scales.