This paper presents a high linearity operational transconductance amplifier (OTA). The OTA circuit combines the techniques of the double differential pairs (DDP) and Source-degenerated current mirrors to achieve high linearity in a large GM tuning range. With the Gm values ranged from 60μS to 130μS, the HD3 of the OTA is below 69dB at 15MHz. The OTA has been applied to a fourth-order linear phase low-pass filter for high speed system. The fourth-order low-pass filter with the cutoff frequency of 15MHz has been implemented. The filter is designed by 0.18-μm CMOS process technology, the HD3 performance is about 53dB, and the group delay variation is below 5% at cutoff frequency.