In order to characterize the anisotropic wet etching rule of quartz crystals, a method to forecast the sidewall profiles of quartz microstructures was studied based on wet etching rates of quartz crystal planes. First, etching rates of quartz crystal planes were summarized and the etching rate vector graphs of crystal planes were plotted for x and y groups. Then, the plane lines denoting their crystal planes were obtained by plotting etching rate vector graphs at each edge of a mask,and the etching shape was the minimum profile enclosed by plane lines. Finally,sidewall profiles of quartz beams at x and y directions were forecasted according to this method. An x direction quartz micro-beam and a y direction quartz micro-beam with a thickness of 500 μm were fabricated after 5 h wet etching process in a mixture of hydrofluoric acid and ammonium fluoride at 70 ℃. Experimental results indicate that -x sidewall of the y direction micro-beam presents a crystal facet with a height of 210 μm and +x sidewall is smooth; and crystal facets with the height of 450 μm and 240 μm appear on ±y sidewalls of x direction micro-beam respectively. These sidewall profiles of the beams are in agreement with the analysis results, which validates the forecasting method of wet etching profile. Results demonstrate that the quartz micromachined structure can be optimized by introducing fabrication processes based on the proposed method in designed steps.