The absorption edge of p-Hg1-xCdxTe with x = 0.7 has been measured at different pressures in the range of 0-36kbar and room temperature. The experimental energy gap is basically in agreement with the result calculated by empirical formula The first order pressure coefficient of Hg1-xCdx Te obtained by a least square fitting to experimental data under different pressures is a = 8.7×10-11eV/Pa, which can be explained by chemical bond dielectric function theory. The second order pressure coefficient of energy gap has also been obtained experimentally as β= -6.3×l0-13eV/ kbar which is hard to understand theoretically. In addition, a structural phase transition has been found under 34-36kbar.