Abstract: We discuss a real-time quality control(QC) procedure for precise point positioning(PPP) with emphasis given to the detection and repair of clock jump,cycle slip detection and robust estimation.Four schemes with different QC procedures are designed to test the effects on PPP.The results show that clock jump should be first compensated during the preprocessing phase since it may cause the cycle slip detection invalid and seriously affect the precision and efficiency of zero-difference PPP.The union of MW and GF combinations can detect the vast majority of cycle slips which is more accurate and reliable than any single one.With an improved robust estimation,gross errors and their impact on positioning are effectively suppressed,which led to significant improvements in the accuracy and reliability of PPP.