Abstract: Hot wire anemometer is used in three typical low speed wind tunnels to measure the flow field turbulence intensity, including a low turbulence wind tunnel, a general closed wind tunnel and an open jet wind tunnel. To deal with the disturbance to the turbulence signal caused by noise, an EMD(Empirical Mode Decomposition) self-adaptive filter and HHT(Hilbert-Huang Transform) time-frequency analysis methodology are introduced in turbulence intensity data processing. The EMD method is compared with several other turbulence intensity processing methods, including BPF(Band Pass Filter), ENC(Electronic Noise Correction) and HPIA(High Pass Inertia Attenuation Filter). Using the EMD filter, the turbulence intensity in the low turbulence wind tunnel test section is measured and found to be less than 0.05% in the flow speed range of 30~100m/s. Using HHT method, we complete the time-frequency analysis of the flow fluctuation signal, and the low frequency flow flucturation signal is found predominatnt in the open jet wind tunnel. The designed EMD self-adaptive filter is effective at controlling the influence of the noise on the hot wire output signal, and therefore it is a practical method for low turbulence intensity signal processing.