An arc-shaped oscillating saw blade with sparse and dense teeth and an oscillating saw are provided. The arc-shaped oscillating saw blade with sparse and dense teeth includes a cutting end composed of a plurality of sawteeth distributed in an arc shape, and a tooth spacing between adjacent sawteeth gradually increases from a middle position to positions at two sides of the cutting end, thus forming a sawtooth arrangement structure with dense sawteeth at a middle and sparse sawteeth at two sides. With a tooth structure with arrangement of proper tooth density gradient, a contact area between the saw blade and a material in the cutting process can be reduced, so that cutting resistance can be reduced. Arc-shaped tooth distribution facilitates improving of the cutting accuracy and surface smoothness, reduces cutting errors and surface defects, reduces impact and vibration in the cutting process, and further improves the cutting accuracy.