Digital sketch is the basis and skeleton of painting; It is also the art of temperance that needs the help of reason most. Beginners must learn to sketch first, and those who sketch well can naturally draw oil paintings well. The origin of sketch generally began in the Renaissance. In fact, Greek bottle paintings and sculptures have a good sketch foundation. The original sketch is considered as a manuscript of painting. For example, to make a mural, we must first have a draft of the idea, then a draft of the sketch, and at the same time, we must have an accurate sketch of the hand and face. Painting murals is used to not looking at the model, relying entirely on the sketches prepared in advance and the painter's memory. Modern sketch is divorced from the original paper and practice, and can be appreciated as a work of art. The attitude of sketch not only cultivates the power of description, but also the ability of modeling. Finally, only sketches can be appreciated as works. On the contrary, just looking at oil paintings can show how accomplished the author is in sketching. So digital sketch is the basis of painting.