Objective To investigate the regular pattern of spectra of critical diseases in the elderly in order to provide some reference for further treatment. Methods A retrospective analysis was performed on the clinical data of 423 elderly patients (mean age 76.79 years, ranging from 60 to 102 years) with critical diseases admitted in Bozhou People’s Hospital from February 2011 to February 2014. The constituent ratio of disease spectra, onset seasons, organ dysfunction and prognosis were analyzed. These 423 elderly patients (＞60 years old, elderly group) were divided into 3 subgroups according to their ages. The other 59 young and middle-aged patients (＜60 years old) were taken as controls (control group). The disease spectra and prognosis were compared among different subgroups. Results (1) In this cohort, circulation system disease (ESD) accounted for 55.8% (236 cases), taking the first place among other system diseases, followed by nervous system disease (NSO, 47.3%, 200 cases) and respiratory system disease (RSD, 40.2%, 170 cases). (2) There were significant differences in the spectra of RSD and digestive system diseases (DSD) and tumors among different age subgroups, but no such difference was found in other system diseases. (3) The RSD had obvious seasonal characteristics. (4) There were 167 (39.5%) patients with 2 and 81 patients (19.1%) with 3 dysfunctioned organs, totally accounting for 60%. The ratio of multiple organ dysfunction was significantly higher in the elderly group than in the control one. Lungs and heart dysfunction ranked the first top two places. (5) There was no significant difference in the prognosis among the different age subgroups. (6) A total of 285 senile patients (68.2%) got better prognosis. Mortality of the top three was cardio- cerebrovascular diseases, respiratory system disease, and cancer in this study. Conclusion Critical illness in the elderly is characterized with complicated disease spectra, quickly changed condition, multiple organ failure, and high mortality. Therefore, we should strengthen the underlying diseases and control of chronic diseases, actively treat the primary disease and pay attention to the protection of organ function at the same time, and timely manage organ dysfunction syndrome.