Thermodynamics of aldol condensation of formaldehyde and isobutyraldehyde (IBD) were studied. With the application of Joback and Yoneda (ABWY) group contribution methods and some other empirical formulas, the basic thermodynamic properties such as Hg,298, Sg,298, Cp of the main product of 2,2dimethyl3  hydroxypropionaldehyde (HPA), the byproducts of neopentylglycol (NPG), hydroxypivalaldehyde (1115 acetate), isobutyl isobutyrate and other substances were calculated. Then, the Hr,Gr, Kp of the main and side reactions were derived. The calculated thermodynamic properties agree well with available literature values, which means that the estimation is reliable. The calculated results show that the main and side reactions are exothermic and can happen spontaneously. Relative low temperature is good for the main reaction, because the absolute enthalpy of this main reaction is lower than that of the side reactions. NPG, 1115 ester, and isobutyl isobutyrate are the main byproducts. The conversion rate of IBD would decrease with the increase of temperature and n(IBD)∶n(HCHO). When the ratio of n(IBD) to n(HCHO) is 0.9, IBD conversion rate can reach 99%. The calculated conversion rates at different ratios of n(IBD) to n(HCHO) agree well with experimental data. The thermodynamic analysis would provide basis for the optimization of industrial HPA preparation.