Several analysis centers(AC) and a product integration and service center have been built by the international GNSS continuous Monitoring and Assessment System (iGMAS) currently.Product integration and service center (ISC) analyzes the quality of product provided by analysis centers,and then reprocesses to generate a combined product.The orbit and clock solutionsare the vital products of ISC and importantfoundation data for satellite navigation and precise point positioning(PPP).First of all,this paper introduces the principles,methods and mathematical models oforbit and clock combination.Then,the precision of combined products and analysis centers’productswith respect to the IGS final is compared and analyzed.Furthermore,the PPP tests are implemented to verify the accuracy and reliability of combined orbit and clock.The results show that the RMSof combined orbit and clock with respect to referenced solutionsis better than the most analysis centers.The static PPP tests provethat the combined orbit/clock consistency is maintained at millimeter level.The standard deviation of singleepoch PPP difference using combined orbit/clock is comparable to the best AC orbit/clock solutions.