The electric heating method is a common method used in the liquid specific heat capacity measurement experiment，a part of the experiment error comes from the changing heating power that leads to difficulty in accurately calculating total quantity of the heat. Based on the Newton's law of cooling，the relationship between the heat capacity of the system and the cooling speed of the system is derived under the condition of different quality of the oil test samples and the measuring scheme for oil specific heat capacity is designed. The experimental result shows that the measuring relative error of the method proposed in the paper can be less than 0.03. The advantages of this method are the operability，simple data processing and anti-interference of unstable heating power.