Objective: To explore the clinical features of 88 patients with myeloproliferative neoplasm(MPN) for analyzing the differences between prefibrotic primary myelofibrosis (pre-PMF), essential thrombocytopenia(ET), overt primary myelofibrosis (overt-PMF), and emphasizing the clinical importance of the diagnosis of pre-PMF. Methods: Eighty- eight patients with MPN at our hospital from January 2015 to January 2018 were enrolled. The clinical data including disease classification, routine blood test, splenomegaly, megakaryocyte count, degree of fibrosis in bone marrow and related gene mutations were collected and analyzed. Results: Of the 88 patients, the median age at diagnosis was 61 years (range 20-88 years), 32(36%) patients were over 65 years old, 46 (52%) were male, and 22 (25%) had splenomegaly. There were 51 cases (58%) with JAK2 V617F mutation, 5 cases (6%) with CALR mutation, 2 cases (2%) with MPL mutation, and 30 cases (34%) with triple negative. There were 20 cases of polycythemia vera (PV), 23 cases of ET, and 45 cases of primary myelofibrosis (PMF), including 23 cases of pre-PMF (51% of PMF) and 22 cases of overt-PMF (49% of PMF). Among all the patients with overt-PMF, the mutation rate of CALR gene was as high as 18% (4/22). Clinical manifestations of pre-PMF is milder than that of overt-PMF, with a lower ratio of low hemoglobin and lower platelet count, and a lower mean lactic acid dehydrogenase (P values of 0.048, 0.034, 0.037, respectively). The clinical manifestations of patients with pre-PMF were similar to those of patients with ET, however, the former had a higher proportion of splenomegaly and leukocytosis than the latter (P=0.043 and 0.007). Follow-up showed that patients with ET had longer survival than patients with pre-PMF (P=0.038). In patients with pre-PMF, triple-negative patients had a lower median age and greater number of splenomegaly than patients with JAK2 mutation (P=0.030 and 0.017). Conclusion: MPN is a group of hematological diseases with heterogeneous clonality. Different clinical manifestations and prognosis are presented in patients with pre-PMF and patients with overt-PMF, and it is necessary to distinguish the two diseases. The clinical manifestations of pre-PMF and ET are similar, but the prognosis is different. It is extremely important to distinguish the two diseases by histomorphological diagnosis combined with secondary clinical criteria.