The content of Fe will affect the hardness of the aluminum alloy, and further affect the working life of aluminum alloy devices. Therefore, the detection accuracy of Fe content in the aluminum alloy is very important. In this paper, the detection accuracy improvement of Fe element in the aluminum alloy by millisecond laser-induced breakdown spectroscopy (ms-LIBS) under spatial confinement combined with support vector machine (SVM) was employed. Under the confinement of the plate space, the millisecond laser-induced aluminum plasma spectrum achieves spectral enhancement and the plasma radiation spectrum stability was improved. The spectral enhancement factors of the four characteristic spectral lines Fe Ⅰ 345.99 nm, Fe Ⅰ 369.51 nm, Al Ⅰ 394.40 nm, and Al Ⅰ 396.15 nm are 2.20, 2.14, 2.28, and 2.41, respectively. The calibration models for quantitative analysis of Fe in aluminum alloy based on external standard method and SVM were established. The standard external method was used to calculate the R², RMSEC, RMSEP, and ARE of the Fe element with the plate space constraint of 0.893, 0.261 Wt%, 0.156 Wt%, 40.977%, and R², RMSEC, RMSEP, and ARE without the plate space constraint were 0.852, 0.337 Wt%, 0.274 Wt%, 42.947% respectively. Under the constraints, the RMSEC of the SVM model was 0.086 Wt%, and the RMSEP was 0.043 Wt%. The SVM method was used to calculate the R², RMSEC, RMSEP, and ARE of the Fe element with the plate space constraint of 0.984, 0.086 Wt%, 0.043 Wt%, 3.715%, and R², RMSEC, RMSEP, and ARE without the plate space constraint were 0.941, 0.134 Wt%, 0.051 Wt%, and 12.353%. The results show that under space constraints, the use of ms-LIBS combined with the SVM method can greatly improve the quantitative analysis accuracy and experimental repeatability of ms-LIBs, and effectively reduce the matrix effect of aluminum alloy, which can meet the trace elements of aluminum alloy Quick check.