Objective To evaluate the relationship between left ventricular myocardial strain and prognosis in patients with light chain cardiac amyloidosis (AL-CA) by three-dimensional speckle tracking imaging (3D-STI). Methods A retrospective analysis was performed on the clinical data of 120 patients with AL-CA confirmed in the hospital between January 2020 and January 2022. According to the results of end-point events, they were divided into survival group (n=82) and death group (n=38). The clinical data, routine echocardiogram parameters [maximum end-diastolic wall thickness of the left ventricular (MLVWT), left ventricular end-systolic volume (LVESV), left ventricular end-diastolic volume (LVEDV), left ventricular ejection fraction (LVEF)] and 3D-STI parameters [left ventricular twist (Ptw), global longitudinal strain (GLS), global circumferential strain (GCS), global radial strain (GRS)] were recorded. The relationship between 3D-STI parameters and prognosis of AL-CA patients was analyzed by COX proportional hazards model. The predictive value of 3D-STI parameters for prognosis was evaluated by ROC curves. Results There was no significant difference in general data (gender, age, heart rate, blood pressure) between survival group and death group (P>0.05). The levels of N-terminal pro brain natriuretic peptide (NT-proBNP), cardiac troponin I (cTnI) and creatinine (CRE) in survival group were significantly lower than those in death group (P<0.05). There was no significant difference in LVESV, MLVWT or GCS between survival group and death group (P>0.05). LVEF, LVEDV, Ptw, GLS and GRS in survival group were significantly greater than those in death group (P<0.05). The sensitivity and specificity of Ptw combined with GLS and GRS were high. GLS was an independent predictor of all-cause mortality. Conclusion 3D-STI can reflect left ventricular myocardial strain in patients with AL-CA, and 3D-STI parameters also have reference value to predict prognosis.