This paper numerically calculates the transverse coherent length in atmospheric turbulence in the horizontal and vertical direction by its formula of integration and computer.The analysis shows that the transverse coherent length decreases by increasing range,and in the horizontal direction it is lcss than in the vertical direction in the same range.Therefore,in the horizontal dircction the effect of atmospheric turbulence is larger than in the vertical dircction.Its contribution makes signal to noise ratio(SNR) decrease in the horizontal direction.