Most data in the literature of code-switching come from spontaneous conversation in daily life, and hence it is interesting to examine code-switching in planned discourse like telecinematic discourse, which, different from everyday communication, is designed by the production team behind the screen to accomplish certain goals and purposes. Under the special sociolinguistic situation of Hong Kong where code-switching frequently appear in everyday conversation, this thesis investigates the code-switching and code-choice in the Hong Kong police film Cold War. On the basis of Conversation Analysis (CA), Markedness Model (MM), and Screen-to-face Discourse Model, the thesis analyzes the effects of code-switching and code-choice in the dialogues of the film, the ways the characters apply code-choice and code-switching in different scenes, and how code-switching functions as a strategy for cinematic characterization, exploring the relationships on the screen and those between the screen and the audience. The code-switching analyzed in this thesis is motivated by the representation of professionalism, the expression of mood, the trigger of action, and the negotiation of relationship. It is found that the employment of code-switching is highly variable with different patterns according to the dynamic encounters of characters with the plot moving Forward. Keywords: code-switching (CS), code-choice, Hong Kong, telecinematic discourse, cinematic characterization