The main sources of uncertainty in heating capacity measurements tested by air enthalpy method were analyzed in this paper.Type A and Type B analyses were carried out for uncertainty evaluation through mathematical model.The mathematical models for the main components of uncertainty of heating capacity were deduced and established based on difference of static air pressure,air enthalpy value,air specific volume and air humidity.The heating capacity measurement uncertainty was calculated based on experimental data,and the complex uncertainty components were evaluated by limit method.Thus,a convenient and reliable method was provided to evaluate the uncertainty for heating capacity measurement.