Abstract: The synthesis by oxidation of p-cresol to p-hydroxybenzaldehyde with dioxygen in alkali-methanol solution was invehgated. As it turned out, p-hydroxybenzaldehyde in 68.5% yield was obtained by using Co(OAc)₂·4H₂O-CuSO₂·5H₂O as a catalyst at 60～70℃, atmosphere for 5h. The two new method for separating reaction products were also studied. One is the complex method of sodium hydrosulfite and p-hydroxybenzaldehyde, in which p-hydroxybenzaldehyde is in higher yield and purity can be obscened by using it to sepalate products at lower conversion of p-cresol. Another is multistage crystal method. in which p-hydroxybenzaldehyde is in higher yield and purity can be obtained by using it to separate products at any conversion of p-cresol.