From indoor experiments， the effects of mix proportion and curing age on unconfined compressive strength of plastic concrete were studied. The pH value and electrical conductivity were measured under the corresponding cement content and curing age. The quantitative relationship between pH value，electrical conductivity and strength of plastic concrete was established. Results show that with the increase of cement content， the strength， pH value and electrical conductivity of plastic concrete increase. With the increase of curing age， the strength of plastic concrete increases， while pH value and electrical conductivity firstly increase and then decrease. Under different cement contents and curing ages， pH value of plastic concrete shows three stages： 11.60-12.20， 12.20-12.35， 12.35-12.80， and there is a good power function relationship between electrical conductivity and strength at each stage of pH value.