In this paper, we construct two sets of vertex operators S₊ and S_? from a direct sum of two sets of Heisenberg algebras. Then by calculating the vacuum expectation value of some products of vertex operators, we get Macdonald function in special variables x_i = t ^i-1 ( i = 0,1, 2,). Hence we obtain the operator product formula for a special Macdonald function P_λ (1,t,,t^n-1;q,t ) when n is finite as well as when n goes to infinity.