给input添加:style="{width: '100%'}"即可
<el-row :gutter="15">
<el-form ref="seForm" :model="selectFormData" :rules="rules" size="medium" label-width="100px">
<el-col :span="3">
<el-form-item label-width="60px" label="年度:" prop="coopname">
<el-date-picker
v-model="selectFormData.year"
type="year"
placeholder="选择年"
:style="{width: '100%'}">
</el-date-picker>
</el-form-item>
</el-col>
<el-col :span="5">
<el-form-item label="合作社名称:" prop="coopname">
<el-input v-model="selectFormData.coopname" placeholder="请输入合作社名称" clearable
:style="{width: '100%'}"></el-input>
</el-form-item>
</el-col>
<el-col :span="7">
<el-form-item label="日期范围:" prop="timerange">
<el-date-picker type="daterange" v-model="selectFormData.timerange" format="yyyy-MM-dd"
value-format="yyyy-MM-dd" :style="{width: '100%'}" start-placeholder="开始日期"
end-placeholder="结束日期" range-separator="至" clearable></el-date-picker>
</el-form-item>
</el-col>
<el-col :span="3">
<el-form-item>
<el-button type="primary" @click="selectForm">查询</el-button>
</el-form-item>
</el-col>
</el-form>
</el-row>