Based on the coupled map lattice models, the mutual relation of spatiotemporally chaotic signals is studied using the symbokic analysis method. Numerical computation results show that the conditional entropy of two directly coupled lattices or that of two indirectly coupled but near lattices has a sharp minimum, whereas the conditional entropy of two distant lattices has no sharp minimun. Thus, the mutual relation of spatiotemporally chaotic signals produced by the coupled map lattice systems can be manifested by the symbolic analysis method.