A geometric model of Vela pulsar wind nebula (PWN) is suggested. The method of determination of leptonic distribution function anisotropy is developed based on the comparison of high resolution roentgen Chandra images of Vela PWN with model predicted images. An angular dependence of distribution function in the nebula rest frame is obtained in the ranges ofangle between particle velocity and pulsar wind direction T: 10q < T < 90q and 130q < T < 160q.