This paper aims to develop a fast, accurate, non-toxic and harmless indicating film as a kind of visual food freshness indicating packaging that can make it easier for consumers to observe the freshness of food. In this paper, the biodegradable chitosan/anthocyanin composite film was prepared based on the casting method, in which the anthocyanin acting as the film substrate, glycerin acting as the plasticizer, and the anthocyanin acting as the indicator. The color performance of the film in different pH solutions and acid/base atmospheres could be regulated by changing the mass fraction of anthocyanins. The experimental results showed that when the mass fraction of anthocyanin was 0.3%, the color of the film changed as the most obvious one from pink to yellowish-brown in the pH solution of 1.68-12.45. Besides, in the atmosphere of hydrochloric acid, it appeared blue-purple, and in the atmosphere of ammonia, it appeared brownish yellow. The prepared indicator film was placed in a glass bottle containing fresh fish, and the film could change the color quickly according to the deterioration of the fresh meat. From the experiment, it can be included that with the extension of time, some alkaline substance released by the fish will change the molecular structure of anthocyanin, and the film can quickly change color in response to the rotting condition of fish, so as to achieve the real-time visual monitoring of the fish freshness.