Objective: To explore the effect of borderline personality on suicidal ideation in patients with bipolar depression and its internal psychological mechanism. Methods: A total of 274 patients with bipolar disorder in a hospital in Nanchang were investigated by Beck Depression Inventory-II (BDI-II), Personality Diagnostic Questionnaire (PDQ-4+), Beck Scale for Suicide Ideation (BSI-CV), Cognitive Emotion Regulation Questionnaire (CERQ) and Interpersonal Problem Scale (IIP-32). SPSS soffware and PROCESS plug-in were used for data analysis and processing. Results: Borderline personality, cognitive emotional maladaptive regulation and interpersonal problems were positively correlated with suicidal ideation (r=0.537, 0.454, 0.432, p<0.001). Borderline personality was positively correlated with cognitive emotional maladaptive regulation and interpersonal problems (r=0.523, 0.520, p<0.001). Cognitive emotional maladaptive regulation was positively correlated with interpersonal problems (r=0.523, p<0.001). Cognitive emotional maladaptive regulation and interpersonal problems played a separate mediating role between borderline personality and suicidal ideation (effect values were 0.661 and 0.312). Cognitive emotional maladaptive regulation and interpersonal problems played a chain mediating role between borderline personality and suicidal ideation (effect value was 0.161). Conclusion: Borderline personality can not only directly affect suicidal ideation in patients with bipolar depressive episodes, but also affect suicidal ideation in patients with bipolar depressive episodes through the individual mediating role and chain mediating role of cognitive emotional maladaptive regulation and interpersonal problems.