Director Sang-ho Yeon didn't have the idea of filming a sequel to the movie "Travel to Busan" at the beginning, because filming required a lot of budget. The plan to shoot a sequel was not realized until the support of the distributor of the movie "Travel to Busan" was obtained. Subsequently, he began to calculate the budget and preparation of the script for the film. The story of the film was conceived from some of the ideas that Sang-ho Yeon thought of when he was shooting the film "Travel to Busan". He sorted out these materials and produced the film's story outline
.
In order to photograph the ruins, about 250 Korean visual effects staff produced 1,300 CG renderings. In 2019, director Sang-ho Yeon completed the production of CG images
. The indoor space of Unit 631 is set as a place with almost no light, and artificial lighting is used to create a cold atmosphere. The art director of the film set up temporary tents and containers. In order to facilitate the movement, he also transformed the bus into a supply warehouse and designed a space where the characters in the film can leave at any time
.
