Tunneling ionization of atoms is the basis of many phenomena and techniques, which requires people to be able to comprehensively understand this crucial physical process. Recent experiments have demonstrated the existence of the nonzero initial longitudinal momentum spread at the tunnel exit. However, the initial longitudinal velocity is usually set to be zero in the adiabatic regime. In this work, we numerically study that the initial longitudinal velocity of ionized-out electrons plays the role in the spiderlike photoelectron momentum distributions in hydrogen atom by using the semiclassical rescattering model and the time-dependent Schrödinger equation. Nonzero longitudinal initial velocity, no matter whether it is an offset or an offset distribution, is considered in the semiclassical rescattering model. Longitudinal cut-plot and transverse cut-plot of the photoelectron momentum distribution are discussed. The final longitudinal momentum of the electron is found to be sensitive to the initial longitudinal velocity, which offers us a method of determining the information about the initial longitudinal velocity from a photoelectron momentum distribution according to this linear relationship. We unveil that either an offset or an offset distribution for the initial longitudinal velocity can perfectly reproduce the same spiderlike photoelectron momentum distributions. The semiclassical results are backed by the full quantum simulation. It is expected that more precise research is required to deepen the knowledge of the initial longitudinal velocity in strong field ionization of atoms.