This paper investigates the online scheduling on an unbounded parallel-batch machine with variable lookahead interval to minimize makespan. Online means that jobs arrive over time. At any time $t$, an online algorithm can foresee the information of the jobs arriving in $(t, t+\Delta(t)]$, where $\Delta(t)=\beta p_{\max}(t)$ is the length of the lookahead interval which is not invariable, $p_{\max}(t)$ is the maximum processing time of the jobs arriving at or before $t$ and $\beta\in(0, 1)$ is a constant. On the general case of processing time, we give an online algorithm which is the best possible for 0<β≤1/6. When the processing times of all jobs are restricted in an interval, we give the best possible online algorithm for 0<β<1.