The crystalline component and crystallization morphology of poly(vinylidene fluoride‐chlorotrifluoroethylene) (P(VDF‐CTFE)) ultrathin film have been investigated. The CTFE segment has been characterized as the crystal composition of the film. For the film on the Si substrate, the nucleation behavior is dominated by homogeneous nucleation to form edge‐on lamellae in the initial stage of crystal nucleation growth. The edge‐on lamella will continue to grow at high crystallization temperature (Tc). However, it will be transformed into flat‐on lamellae at low Tc. For the film on Au substrate, the primary nucleation rate of the layer near the film surface has a competitive relationship when compared with the primary nucleation rate of the layer near the film/substrate interface. The nucleation behavior is preferentially dominated by heterogeneous nucleation to form flat‐on lamellae at high Tc. But it is conducive to homogeneous nucleation to form edge‐on lamellae at low Tc. Further investigation suggests that the different crystalline morphologies of P(VDF‐CTFE) ultrathin film obtained on Au and Si surfaces are closely related to the different interface effects between the film and the substrates. It is anticipated that this study will cast new light on the rational regulation of the morphologies of ultrathin films.