  In the paper the nilpotent conditions of BRST operator for new superconformal
string model were found. This string includes anticommutation $2-d$ fields
additional to the standard Neveu-Schwarz superconformal set which carry quark
quantum numbers. In this case the superconformal symmetry is realized by a
non-linear way. In the superconformal composite string new constraints for 1
and 1/2 conformal dimension should be added to the standard system of Virasoro
superalgebra constraints for 2 and 3/2 conformal dimensions. The number $N$ of
the constraints and numbers $D$ and $D'$ of bosonic and fermionic $2-d$ fields
are connected by a simple relationship $D'/2+D-3N-15=0.$ Also perspectives of
the critical composite superconformal string are discussed.
