Based on model approximation, the problem of stability analysis for uncertain fractional order systems with time-varying delay is proposed. Firstly, a rational approximation method is introduced for fractional order systems. Based on the above method, the fractional order systems are transformed into the integer order systems whose uncertainties are approximation error. Afterwards, integral inequality approach is used to analyze the stability of the approximation system, obtaining a robust stability criteria denoted by LMI. Theoretic proof and numerical examples are provided to illustrate the effectiveness and the availability of the proposed method.