Physical equations, numerical methods and slide grids of laser ablative hydrodynamic instability in the code EUL3D are introduced. Simulation results of the EUL3D code are good agreements with those of the Takabe formula, the FAST2D code and the LASNEX code, and the experimental result of laser ablative RayleighTayler instability in Osaka University. The lower Atwood number stabilization due to the preheat is observed in simulation and a new growth rate formula is obtained. It includes the density gradient, the lower Atwood number and the ablative convection stabilizations, so it agrees well with all of 2D simulations．