This paper use the MLFMM algorithm in Altair FEKO,gives the calculation detail of lens antenna model in terahertz band.By combining FEM and MLFMM,we design and analysis the lens integrated planar log periodic antenna,and obtain the return loss,near and far field radiation characteristics.Calculation shows that the antenna return loss is lower than 10 dB,and the average gain is 28 dB,with good symmetry and high bandwidth.