The invention relates to a construction method of a dam foundation pit waterproof curtain for sand gravel and dolomite crushing zones. The construction method comprises the following steps that a damfoundation pit is digged, a first-stage anti-seepage net is constructed on the inner wall of the foundation pit, and a second-stage anti-seepage net is built in the foundation pit. According to the technical scheme, pilot hole drilling exploration is adopted in the construction process according to complex geological condition characteristics, then the optimal construction method is selected according to different rock-soil property conditions in combination with the actual geological condition, so that high-efficiency construction is realized; a long-arm spiral drilling machine is very fast to use in the construction process, and quality is guaranteed; meanwhile, the connection length and the connection time between piles are reasonably controlled, so that the connection section quality between different construction areas is improved, anti-seepage axes of the anti-seepage nets at all levels are optimized, the anti-seepage workload and the area of water seepage areas of the foundationpit are reduced, and conditions are created for drainage of the dam foundation pit; and compare to the prior art, the raw materials are greatly saved, and cost of the later-period frequent drainage is reduced.