A waterproof paint formula and a pen device for using the same. The concentration of the formula may be adjusted by changing the weight percentage of the aqueous solution and cooperate with different outlet diameter of the nibs to make the waterproof paint smoothly flow out for painting on the writings. Simultaneously, the weight percentage of Ethyl Alcohol may be adjusted to control the air-dried speed of the waterproof paint to achieve the effects of waterproof and preventing the inks or colors from diffusion.