Monet is a representative figure of impressionist painting and one of the most influential impressionist masters. He devoted his life to impressionist techniques. Monet's paintings, whether sketched on the spot or finished indoors, give people the characteristics of one go, strong randomness and focus on capturing the overall charm of objects. There are not too many restrictions on the choice of scenery materials. It looks casual when you are in a mood, but in fact you use scenery to express your feelings. Its freehand brushwork is close to our traditional aesthetic habits, which may be one of the reasons why impressionist painting is more easily accepted by the public in China. Monet's "freehand brushwork in color" can be demonstrated by his superb ability of "color expression" and "shaping with pen" The "color" and "pen" of oil painting are equivalent to the "pen and ink" of Chinese painting that we have always emphasized. In this sense, Monet is undoubtedly a master of using pen and ink in oil painting. In Monet's works, the sunrise is boundless, the smoke is misty, and the drizzle is blurred ... those poetic and picturesque scenes are vividly expressed by him. He developed a very free and skilled technique of writing with a pen. Sometimes it's a thick color, sometimes it's a light color, sometimes it's a light cover, and sometimes it's like flying ... it changes with gender. Monet paid more attention to light color and artistic conception than to objects. He simplified and even blurred the shape and structure of the image, and melted the appearance of the image into light color, thus giving the image a unique poetic beauty. The series of Water Lily in his later years can better reflect his good use of pen and ink and his freehand brushwork of color. During the period of 1903- 1908, Monet painted about 48 water lilies, which he named "Water Lily Waterscape Series". Especially in the last 12 years of his life, he finished his largest mural work "Water Lily". "Water Lily" can be said to be Monet's summary of the expression of light and color in his life, and it is also Monet's most outstanding work showing freehand brushwork characteristics.