A single load microcalorimeter with auto-feedback is constructed as the national coaxial primary standard for broadband power of China.A temperature-compensated coaxial themistor mount is used as working standard inside.The effective efficiency of the working standard is calibrated from the RF power loss in the mount which is measured by a calorimetric method.The part of RF power loss in the mount wall is measured with the temperature-compensation themistor in the mount instead of traditional thermal coupler method.The new method has advantages of short response time

high sensitivity and simple structure.Implement method and uncertainty analysis of the power standard is presented in detail.International comparison data and figures are also included for confirmation of the power standard accuracy.