Sketch is the simplest form of land reclamation in art, and sketch in a broad sense refers to all monochrome paintings; Sketch in a narrow sense refers to the painting training process used to learn art skills, explore modeling rules and cultivate professional habits. Art is a means to express things. The foundation of art is modeling, which is a complex labor carried out by people in a natural way and a special skill that needs long-term training. Artistic modeling is not only to shape isolated and static object forms, but more importantly, to express the organic relations of various forms in objects. To master the method of artistic modeling, we should not only restore people's natural way of thinking and operation, but also study the formal characteristics of natural objects and understand their changing laws and conditions. Sketch is the best way to solve these modeling problems, which has been fully proved in the practice of artistic modeling. Therefore, sketch is called "the foundation of plastic arts".

The foundation of sketch comes from the simplicity and flexibility of making tools and the simple popularization of research objects.

Sketching tool is the simplest modeling tool, with only paper and pen. Primary sketch training is done with pencils. The tool is flexible to use and easy to modify. It can not only show small changes, but also draw a large area of gray. You can practice for a short time and do your homework for a long time, which is very suitable for beginners to learn and master sketch modeling methods repeatedly.

The object of sketch research is the basic form and general change law of objects. The basic form includes the proportion, shape, brightness and other structural forms of objects, and the changing law includes visual factors such as contraction and parallax contrast. Mastering these forms and laws is the premise of modeling, and sketch can take advantage of its long-term repeated training to solve these situations one by one.

Sketch can not only solve the basic and general problems of modeling, but also solve the application and special problems of modeling. For example, the change and unity of modeling, overall structure, observation and operation methods, generalization and beautification, emotional expression and so on. It can be said that sketch is a modeling form with simple tools and rich forms of expression, which can complete the modeling learning task from primary to advanced. Therefore, learning art should start with learning sketch.