Aiming at the shortages of constraints solving in collaborative design, an interval narrowing algorithm based on constraint bintree was put forward, in which two processes were included, namely the forward interval expanding operation from bottom to root of constraint bintree and the backward interval shrinking operation from root to bottom of constraint bintree. Then a constraint solver has been developed to solve the public solution space of the multi-disciplinary constraints. Using this method can avoid introducing the internal variables and decomposing the constraints into solution functions, improve solving efficiency and easily implement symbol calculation automation.