This paper makes the following investigations. 1. To solve the second open problem proposed by M.Morii and M.Kasahar[1]; 2. To prove the nonexistence of PSSP sequence with the smallest(or biggest) density; 3. To find the PSSP sequence with (complementary) Hamming weight m for every positive integer m; 4. To propose a generalization form of the known IYM sequence.