The invention relates to a partial tunnel excavation construction method for enlarging wall feet. The method comprises the steps that firstly, a part at the left side of the upper portion of a headingis excavated, and an initial support and a temporary support are constructed on the part; secondly, a part at the right side of the upper portion of the heading is excavated, and an initial support is constructed on the part; thirdly, an arch foot part at the left side of the lower portion of the heading is excavated, and an initial support, a secondary lining and filling-layer concrete are constructed on the part; fourthly, an arch foot part at the right side of the lower portion of the heading is excavated, and an initial support, a secondary lining and filling-layer concrete are constructed on the part; fifthly, after the concrete strength of the arc foot part at the right side of the lower portion of the heading reaches preset strength, the temporary supports are demolished; sixthly,a part in the middle of the lower portion of the heading is excavated, and an initial support, a secondary lining and filling-layer concrete are constructed on the part; seventhly, after the whole surrounding rock and the initial supports are stabilized, waterproof layers and drainage pipes are laid, and pouring are conducted on the overall secondary linings at the upper portion of the heading. Bymeans of the method, not only are the whole processes of partial excavation optimized, but also the construction progress is accelerated, and the cost is saved since the temporary supports do not need to be connected to the arch bottom.