Now developing ultra high voltage grid, on the measurement precision and speed of the current transformer is put forward higher requirements. When the input current signal to noise ratio is extremely low, Optical current transformer (OCT) is difficult to from the point of view of frequency domain filtering .So putting forward without trace particle filter (UPF) to improve the signal-noise separation ability of OCT, and focus on poor real-time performance of large conventional UPF computation problems, Put forward improved UPF filtering based on global real-time sampling to improve filtering. Then discussing the three-phase short-circuit power system , the effect of this filtering, Put forward further improvement by using residual error as threshold to calculate. Finally simulation in the Matlab, results showed that the improved UPF method based on global sampling off the ac/dc component accurately, effectively improve the output SNR and filtering accuracy, and short circuit conditions, also can rapid, accurate filtering for relay protection device to improve current.