Since modern architectural technology has set a new standard for toughness of mortar, expensive polymer admixture has been used to modify dry-mixed mortar currently. But high cost critically restricted popularization of dry-mixed mortar. A new expanded Perlite powder- redispersible Polymer powder Compound dry-mixed mortar Admixture (PPCA) was researched in this paper. The research has indicated that PPCA showed synergistically optimized effect. There was the best modification effect when expanded perlite powder/redispersible polymer powder rate was 2 and admixture/cement rate was 0.15. The Ratio of Compressive strength to Flexural strength (RCF) declined to less than 3 when compressive strength of mortar staying above 10MPa. Moreover, cost of this compound admixture only was 1/3 of redispersible polymer powder admixture of the same performance. Meanwhile, this PPCA can improve water retention and increase softening coefficient of mortar to above 1.