Objective To investigate the application value of B-type natriuretic peptide in patients with dyspnea. Methods 110 cases with dyspnea in our hospital from February 2015 to February 2016 were selected and divided into two groups. Patients with pulmonary dyspnea were seen as observation group. Patient with cardiac dyspnea were seen as control group. There were 59 cases in control group. According to ACC Heart Function Classification Standard, there were 25 cases with class II, 21 cases with class III, 3 cases with class IV, there were 51 cases in observation group; collect the venous blood of the two groups, using ECL to detect the natriuretic peptide content in plasma, using color doppler sonography diagnosing to detect the left ventricular ejection fraction and left ventricular end-diastolic diameter. Results Left ventricular ejection fraction and BNP level of control group were higher than observation group, left ventricular end-diastolic diameter of observation group was lower than control group, the difference was statistic significant(P<0.05). In patients with different cardiac functional grading in control group, with the increasing of cardiac function, left ventricular end diastolic diameter was increased and left ventricular ejection fraction was declined, BNP in serum was increased. Conclusion For patient with dyspnea, measurement of B-type natriuretic peptide content can be used to diagnose severity of illness. BNP content can be used to confirm the reasons of dyspnea. Positive expectant treatment can improve dyspnea and is conducive to patients ' prognosis.