Abstract: To solve the problem that the exhaust steam from the back pressure steam turbine（BPT） can not enter into the heating header with the decreased pressure in a 1 000 MW thermal power unit under deep peak regulation condition, a retrofit was conducted on the exhaust steam of the BPT by adding the extraction pipeline from the high temperature reheater steam tube, while the heating capacity of the unit was analyzed and calculated with different opening degrees of the intermediate pressure（IP） control valve. Results show that, with the improved pressure of the high temperature reheater by decreasing the opening degree of the IP control valve, the BPT can operate safely and continuously under deep peal regulation condition. Additionally, the heating capacity is improved by extracting steam from the high temperature reheater. When the unit load reduces to 350 MW, the mass flow of the heating extraction steam can reach at 115 t/h with the heating steam pressure of over 1 MPa and the heating steam temperature at around 320 ℃.