Syntactic structures production (in particular phrase syntactic structure) according to X-bar theory is carried out through two principles: the existence of Headedness and Binarity principles. According to the first one, which is this study’s concern, phrases are projections to grammatical heads. In addition, the grammatical heads which they acquire complements to form phrase projects, store in the mental lexicon syntactic information as to the type of the complements without the determination of the heads location: whether they precede or succeed the complements. However, the determination of the grammatical heads position within a phrase project of a language is concluded by head parameters in syntax, as they located either at the beginning or end of the project. Initially, according to the X-bar theory, the grammatical heads were solely limited to lexical categories, yet a part of the functional categories later on has been considered grammatical heads as well. In this study, which deals with head parameters in functional phrases in Kurdish language, we have specified Tense, Agreement and Complementizer categories as grammatical heads of functional projections of (TP), (AGRP) and (CP). We have also demonstrated through examples and diagrams, the type of head parameters that each projection applies.