ABR (available bit rate) flow control is an effective measure in ATM network congestion control and traffic management. In large scale and high-speed network, the simplicity of the algorithm is crucial to optimize the switch performance. Though the simplicity of binary flow control is very attractive, the queue length and allowed cell rate (ACR) controlled by the standard EFCI algorithm oscillate with great amplitude, which has negative impact on the performance, so its applicability is doubted, and then relatively complex but effective explicit rate feedback algorithms are introduced and explored. In this study, based on the existed flow control model, the performance of standard EFCI algorithm is evaluated and analyzed with the describing function approach in nonlinear control theory, concluding that queue and cell rate self-oscillations are caused by the inappropriate nonlinear control law originated from intuition, but not intrinsic attribute of the binary flow control mechanism. The simulation experimental results are done to validate this analysis and conclusion. Finally, a parameter settings scheme is put forward to optimize the existed EFCI switch.