In the planet formation process, dust grains must grow from (sub-)micron sizes to form millimeter-sized chondrules and eventually kilometer-sized planetesimals. Observational constraint on maximum grain size is essential to understand the planet formation process because it concerns our interpretations of grain growth efficiency, dust stickiness, and mass budget in the protoplanetary disk. We intend to give the constraint by a statistical study of (sub)millimeter spectra of protoplanetary disks which reveal the dust properties. Here we present the SMA 200-400 GHz surveys towards a sample of 47 Class II disks in the Taurus-Auriga region. The low (~2) mean spectral index in our sample indicates the emission is contributed by the high optical depth disk surrounded by the optically thin halo. We also obtained the spectral indices variation along the frequency, which may be due to the scattering opacity dominating when the maximum grain size is ~0.1 mm or due to the higher ratio of emission from optically thin halo at high frequency. Our analysis results may provide a broad implication for the dust stickiness and mass budget.